# Collegeboard and the AP Calculus exam is done!

1. May 5, 2004

### Ebolamonk3y

Do not talk about the Mulitiple choice exam.

DO NOT TALK OR CONVEY OR ALLUDE TO THE MULTIPLE CHOICE PORTION OF THE EXAM AT ALL! Discussions of the Free response is permitted as of Friday or 48hours from 8AM Wednesday 5/5/04

That is not allowed because they recirculate that year after year. But how did everyone do on the Free response portion of both AB and BC exams? :)

I thought the BC no calc was hard as SHlT and the with calc was piece of cake.

Last edited: May 5, 2004
2. May 6, 2004

I've heard differing opinions about the calc test. Some people have said it was pretty easy and some others have said it was tough.

3. May 6, 2004

### Ebolamonk3y

:) good stuff.

4. May 6, 2004

### Ebolamonk3y

Alright... Its officially 48hours after the AP Calculus BC Free response stuff...

How did everyone do?

I thought the Part II no Calculator part was harder than the 1st with calculator part...

Question one took the longest time with that differential equations. And I got 12 and 12 for the limits as t approaches infinity.

Last edited: May 7, 2004
5. May 7, 2004

### Theelectricchild

I took BC last year--- the added series part of the exam are only there to boost my grade.

I love series.

6. May 7, 2004

### Ebolamonk3y

:) You a Ramanujan Jr?

7. May 10, 2004

Has anyone worked out the answers to the AP Calc. AB free response problems yet? I'm trying to gauge how I did, but I don't know if what I'm doing is correct or not (obviously, or I wouldn't be asking for others' answers). They can be found at http://www.collegeboard.com/student/testing/ap/calculus_ab/samp.html for anyone wanting to look at them.

Last edited: May 10, 2004
8. May 11, 2004

Why don't you post what you did and we'll check 'em for ya', instead of us doing all the work you've done already all over again.

9. May 11, 2004

### Ebolamonk3y

Last edited by a moderator: Apr 20, 2017
10. May 11, 2004

### Theelectricchild

Looking at the second problem on this test, it angers me how my Calculus III course last quarter never went over Taylors Inequality and overall applications of Taylor Series...

11. May 11, 2004

### Ebolamonk3y

Not a Calc III topic :) Its not that bad... Just take a look at a it for a while...

12. May 11, 2004

For test AB, Form A, my answers...

1.
a.) 2474 cars (integral of F(t) from 0 to 30)
b.) Traffic flow is decreasing because F'(7) -1.873 < 0
c.) 81.899 cars/minute (1/(15-10) * integral of F(t) from 10 to 15)
d.) 1.518 cars/minute^2 ((F(15)-F(10))/(15-10))

2.
a.) 1.133 (integral of f(x) - g(x) from 0 to 1)
b.) 5.150 (integral of (2-g(x))^2 - (2-f(x))^2 from 0 to 1)
c.) no idea :-/

3.
a.) -.133
b.) Speed is increasing because a(2) < 0 [a(2) = -.133] and v(2) < 0 [v(2) = -.436].
c.) The particle reaches its highest point when velocity = 0 because the velocity function is the deriviative of the position function, resulting in a critical point where v(t) = 0. v(t) = 0 at time t=.433.
d.) NOT SURE BUT...The position at time t = 2 is -1.361, and is moving away from the origin because both its position and velocity is negative. (Position found by the integral of v(t) from 0 to 2, -1 because the position at time t = 0 is -1).

4.
a.) Just a proof, no problem there.
b.) The y coordinate is y = 2.
c.) The d2y/dx2 at point P is -2/7. Point P is a local minimum because -2/7 < 0.

5.
a.) g(0) = 9/2, g'(0) = 1
b.) Sort of a guess because of a lack of time: x = 2
c.) Didn't get to it.
d.) Didn't get to it.

6.
a.) [Slope field sketched].
b.) The slope is positive where y > 1 where x != 0.
c.) y = e^(x^3/3) + 2 [I think I was supposed to put the C as a constant infront of the e but was once again pressed for time and did it the fastest way possible.]

13. May 11, 2004

### Ebolamonk3y

I noticed also that even AP teachers had much difficulty with this problem... On the AP Listserv they were always comparing answers to what is and what was because the answer keys are not posted just yet... There is, just like here, some complaint about somethings that regular Calc students should not get as a student, etc...

14. May 16, 2004

### kvzrock

some error corrections:
b) should be 5.15pi. Forumula for solids of rev. disk method : pi*integrate( (r1^2 - r2^2) dr )

d2y/dx2=-2/7 <0 hence the curve is concave down therefore it is a local maximum

Last edited: May 16, 2004
15. May 9, 2006

### lilartsychic

hey, does anyone have the answers to the part II's for calc AB for form B

16. May 10, 2006

### mathwonk

I am a university calculus teacher and the AP tests you referrred us to look very tedious to me. Here is the kind of test I have given my hoinoirs classes at nuiversity in calculus:

do they look easy to you? I am just curious.

2310H Test 2 Fall 2004, Smith NAME:
no calculators, good luck! (use the backs)
1. (a) Give the definition of "Lipschitz continuity" for a function f on an interval I.

(b) State a criterion for recognizing Lipschitz continuity in the case of a differentiable function f on an interval I.

(c) Determine which of the following functions is or is not Lipschitz continuous, and explain briefly why in each case.
(i) The function is f(x) = x^1/3, on the interval (0, ).

(ii) The function is G(x) = indefinite integral of [t], on the interval [0,10], (where [t] = "the greatest integer not greater than t", i.e. [t] = 0 for t in [0,1), [t] = 1 for t in [1,2), [t] = 2 for t in [2,3), etc....[t] = 9 for t in [9,10), [10] = 10.)

(iii) The function is h(x) = x + cos(x) on the interval (- inf,+inf ).

2. (i) State the "fundamental theorem of calculus", i.e. state the key properties of the indefinite integral function G(x) = indefinite integral of f from a to x, associated to an integrable function f on a closed bounded interval [a,b]. You may assume f is continuous everywhere on [a,b] if you wish.
(ii) Explain carefully why the definite integral of f from a to b, of a continuous function f, equals H(b)-H(a), whenever H is any "antiderivative" of f, i.e. whenever H'(x) = f(x) for all x in [a,b]. Justify the use of any theorems to which you appeal by verifying their hypotheses.
(iii) Is there a differentiable function G(x) with G'(x) = cos(1/[1+x^4])?
If so, give one, if not say why not.

3. Let S be the solid obtained by revolving the graph of y = e^x around the x axis between x=0 and x=3. Define the moving volume function V(x) = that part of the volume of S lying between 0 and x. (draw a picture.)
(i) What is dV/dx = ?
(ii) Write an integral for the volume of S, and compute that volume.

4. The accompanying picture is supposed to be a pyramid of height H, with base a square of side B. Define a moving volume function V(x) = that part of the volume of the pyramid lying between the top of the pyramid, and a plane which is parallel to the base and at a distance x from the top.
(i) Find the derivative dV/dx. [Hint: By similarity, b/B = x/H.]
(ii) Find the volume V(H).
(iii) Make a conjecture about the volume of a pyramid of height H with base of any planar shape whatsoever, and base area B.

Either: Prove the FTC. from part 2(i), you may draw pictures and assume your f is monotone and continuous if you like.

17. May 10, 2006

### mathwonk

[Recall that a lower bound for a sequence {sn}, n ≥ 1, is a number K such that for every n≥1, we have sn ≥ K; and that a greatest lower bound for {sn}, is a lower bound such that no larger number is a lower bound.]
Assuming that {sn} is a weakly monotone decreasing sequence of reals, and that L is a greatest lower bound for {sn}, prove {sn} converges to L.

2.(i) Use an appropriate comparison test for series with positive terms to verify the series for ex: 1 + x + x^2/2! + x^3/3! + .... , converges absolutely for any fixed x.

If a sequence {fn} of continuous functions on [a,b] converge in the sup norm to a continuous function f, then prove the indefinite integrals of the fn also converge in the sup norm to the indefinite integral of f.

a) If f is a continuous function on the reals, with f(1) = c > 0, what else must be checked to conclude that f(x) = c^x for all x?

b) If a,b are positive numbers, use the method above to prove that the function f(x) = a^xb^x, equals (ab)^x.

If f is defined by f(x) = 1/2 for 0 ≤ x < 1/2; f(x) = 1/4 for
1/2 ≤ x < 3/4; f(x) = 1/8 for 3/4 ≤ x < 7/8; .....; f(x) = 1/2^n for
(2^(n-1) - 1)/2^(n-1) ≤ x < (2^n -1)/2^n; and f(1) = 0, explain why f is integrable on [0,1], and compute the integral. (The FTC is of no use.)

X. We know any function f: R+-->R which is
(i) continuous, (ii) not always zero, and (iii) satisfies f(ax) = f(a) + f(x) for all a, x >0 is a “log” function. Using this, prove that f(x) = integral of 1/t from t=1 to t=x, is a log function, using appropriate theorems. [Hint: You will need to show f’ exists and then compare the derivatives of f(x) and f(ax).]

XI. We know the only function f such that (i) f is differentiable, (ii) f(0) = 1, and (ii) f’ = f, is e^x. Assuming an everywhere convergent power series is differentiable term by term, prove the sum of the powers x^n/n!, for n non negative, converges to e^x. [Hint: First prove it converges everywhere.]

these tests were given to incoming freshmen taking second semester calculus with AP backgrounds.

Last edited: May 10, 2006
18. May 10, 2006

### mathwonk

extra credit: prove e is irrational by showing

n(1 + 1 + 1/2! + 1/3!+....) cannot be an integer for any positive integer n.

19. May 10, 2006

### mathwonk

thanks for showing us these tests. as a college teacher i am benefited by knowing what kind of questions AP students are being asked.

i myself do not consider these tests easy for the most part ok, in a few cases, like what value of y makes y' = (y-1)^2 g(x) equal to zero). But there is nothing deep in them. and they do not greatly resemble the kind of tests i give in college. this claim by the AP people is false.

my tests are both easier and harder. they involve easier calculations but harder ideas.

these AP tests have a very high schoolish feel to them, in that the difficulty is all in the details, not in the concepts. I.e. these are questions about elementary ideas which are made technically hard, by using complicated figures or functions, and involving many steps.

Asking you to integrate a function that has 5 different formulas for its definition over an interval is not my idea of an interesting problem. note however that my own test has a similar problem, but in mine, there is pattern to the different formulas, and the integral turns out to be the sum of a series.

moreover in mine the concept is deeper because my function is not continuous, and it helps to know that any monotone function is integrable.

these problems are typical high school contest problems in that they test cleverness and complicated calculations as opposed to depth of understanding. I remember these from my high school, math contests days.

this may be a good thing, as young kids find this kind of competition fun, but it is not true that it resembles what I want my college students to know. I was good at these trick questions, and I preferred it, as that was easier than learning the ideas by studying hard and thinking. I even won prizes at it, in fact I was state champ at some such stuff, but I was not ready for college math.

I want my students to understand what integration means, and which functions are integrable, and why, not just be able to calculate tricky integrals.

I might ask a beautiful and surprising integral, like proving the surface area cut from a sphere by two parallel planes depends only on the distance apart of the two planes.

it is well known that archimedes was proud of calculating the ratio of the volumes of a sphere and a cylinder containing it exactly. but it is also of interest that the surface area of the sphere is the same as the lateral surface area of the cylinder, and that in fact any two planes parallel to the ends of the cylinder cut the same area on cylinder and sphere.

it is also helpful to understand why archimedes was able to calculate the area under a parabola as well as the volume of a sphere, and also the sum of the squares of the first n integers,..they are all the same problem! do you see why?

they offer us college profs $1500 a week to come and grade these tests but after seeing one, I would not do that torture for much more money. you should be proud of yourselves for being smart enough to do well on these tests, but do not be fooled into thinking good college courses are like these. Of course the more stduents come in with this background, the more we may alter our courses to accomodate them, but there are a lot of solid, deep, courses out there that involve proof, discovery, and hartder ideas. I hope you encounter them as you are likely among the future mathematicians and scientists. Last edited: May 10, 2006 20. May 10, 2006 ### Cincinnatus I've seen you mention lipschitz continuity several times on this board mathwonk... what is it? I was never taught anything about it. 21. May 10, 2006 ### mathwonk lipschitz continuity means the ratios deltay/deltax are bounded on the whole interval, or equivalently for functions that have derivatives, the derivative is bounded. that is the most important kind of continuity for integration. most books restrict their attention to continuious functuions for integration, but of course many discontinuous functions are integrable. after all integration is about finding area, and anyone can find the area of a rectangle, and yet every year I have students tell me that the function with value 1 on the interval [0,2) and value 2 on the interval [2,3] is not integrable because it is not continuous. note that the graph is composed of rectangles so any moron can find the area. That is the kind of nonsense that comes out of some AP calculus (and some university) instruction. I am as interested in having my students think as in having them become little calculators. after all a$10 calculator can outstrip anyone at the latter, so how wil they live if they are thoughtless automatons?

now in order to understand riemann integration, not only does one want to understand which functions are integrable, but also what kind of functions can be integrals. we all know that the indefinitye integral of a continuous function is differentiable, but how many have noticed that the integral of any integrable function is always continuous, even if the original function was not?

but more is true, an integral is always lipschitz continuous which is much stronger. if |f| is a bounded function, say by K on the interval [a,b], and G is its indefinite integral, then deltaG/deltax is also bounded by K. so G is actually lipschitz continuous, which is much stronger even than uniform continuity.

suppose you want to mimic the FTC for integrable, not just continuoius functions? i.e. if f is only integrable, it is obvious that the integral of f on [a,b] equals G(b)-G(a), where G is the indefinite integral if f, i.e. where G(x) is the integral of f from a to x. But how do we recognize G in order to make use of this?

I.e. in the usual FTC, where f is continuous, we look for a function G that is differentiablke and has derivative equal to f everywhere. But what if f is only integrable, e.g. monotone? How do we find G?

It turns out that integrable f's are continuous almost everywhere, so the G we seek will also be differentiable almost everywhere, with derivative equakl to f where f is continuous. But what else should we require of G?

Well of course it makes sense to ask for G to be continuous, but this si not enough!

22. May 10, 2006

### mathwonk

I.e., there exist continuous functions with derivative equalk to f everywhere f is continuous, but which diffewr from the integral of f. The key is to require lipschitz continuity.

I.e. to recognize the indefinite integral G of an integrable f, lok for a lipschitz continuous G such that G is differentiable wherever f is continuous, and G'(c) = f(c) at such points.

The point is this is what is needed to rpove the mean value theorem. I.e. what is needed to prove the FTC is the knowledge that a function with derivative zero everywhere is constant. But this si not true for functions whicha are differentiable only most ofthe time. But for a lipschitiz continuous function, having derivative equal to zero most of ttime is enough to force it to be constant. hence this is the right idea.

why would someone not mention lipschitz continuity in an integration course, when that is the concept that distinguishes integrals?

23. May 10, 2006

### mathwonk

the upshot of not teaching this idea, is that 5 or 6 years later when students take real variables, and learn that a funtion is the indefinite inetgral of a lebesgue integrable function if and only if it is absolutely continuous, (a generalization of lipschitz continuity), they have no idea where this came from.

also when they study differentiable equations, and lipschitz vector fields emerge as the natural ones for which the solutions are unique, they have no clue why. i.e. the MVT is the key to uniqueness of soluition of equations like G'=f, G(0) = a.

thanks for the question. am i making any sense?

by the way i myself learned these ideas by teaching out of good books in honors calc, like Courant and John. it made me so happy to realize that after 40 years I had finally understood the claptrap about absolute continuity and the radon nikodym theorem that I was taught in graduate reals, i tried to re introduce these basic ideas into calculus at the beginning.

back when riemann defined integration, he proved on the next page that a function is riemann integrable if and only if the set of discontinuities has measure zero, but the gap between this fact and the definition has now reached 6 or 8 years in school, and is almost reserved for math PhD candidates. (But you do get it in spivak's calc book.)

i still remember the shocked and happy look on one of my honors calc, post AP, students faces when he asked me, after we had noted that all monotone functions are integrable, exactly which functions are riemann integrable, and i told him.

Last edited: May 10, 2006
24. May 10, 2006

### mathwonk

now you might think a student can wait for these subtleties, but how long should they wait to realize that after taking a calculus course they should not claim that a rectangle has no area. it is this sort of thing that got me started.

the point is whether a course is about understanding ideas, and why?, or about making highly tedious calculations that any calculator can do better.

25. May 10, 2006

### mathwonk

here is another reason to teach lipschitz continuity: it is easier and more basic than regular continuity, and implies it.

e.g. the fact that deltay < K delta x, makes it trivial to see that deltay gets small as deltax does, and easy for anyone to compute the delta that goes with a given epsilon, when doing the feared epsilonics that students find so hard.

I.e. if delta y changes no more than K times as fast as delta x, then obviously the right delta to choose is epsilon/K.

anyone can do this.

suppose we are trying to find the right delta to go with a given epsilon to prove continuity for the function f(x) = x^3, at say x = 2. just note that [x^3-a^3]/(x-a) = x^2 + ax + a^2, so for a and x on the interval [1,3] say, this is bounded by 3(3)^2 = 27. so just take delta < epsilon/27.

i.e. almost all functions actually met in courses are in fact lipschitz continuous, so the method is available.

moreover the ease of the comparison between deltax and delta y for these fucntions helps make the point about what continuity means, not that "you can draw the graph without pickling up your pencil."

that intermediate value version of continuity does not convey the essential apporoximation property of continuity so useful to physicists and applied mathematicians, and everyday persons, i.e. the fact that changing the inputs a little only changes the outputs a little.