# Darivative problems! which one is wrong?

## Homework Statement

http://img197.imageshack.us/img197/8162/probc.jpg [Broken]
http://img197.imageshack.us/img197/8162/probc.jpg [Broken]

in the picture

## The Attempt at a Solution

i am not sure about the 4th and 6th ones but i am almost 100% sure that everything else is right.
can you please explain to me which one is wrong?

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Two of your answers are incorrect. Question 4 is correct, but question 6 is not. Use the hint in number 6 and let x = 0. Do you see why it must be false? I leave you to find the other incorrect answer.

--Elucidus

Two of your answers are incorrect. Question 4 is correct, but question 6 is not. Use the hint in number 6 and let x = 0. Do you see why it must be false? I leave you to find the other incorrect answer.

--Elucidus
oh that makes sense.. if u plug in 0, f+g will equal 0 too... which means the derivative is gonna be the same....
i get it.........

now i am sure that everything is good.... but the last one is tricky.. should be right though..
f(x) the derivative is f'(x) not g(x) so that must be false.
maybe the 3rd one? even though i read about it.. and if u plug in e^x, it should stay the same..

For the last one, it might be easier to write it out as.
f(x) = pi x^-2

Find the derivative, see if it matches.

For the 3rd, try out a few other possibilities. You should point out to your teacher that when a=e, that e^x works.

oh... that why i got it wrong because i assumed that i can plug in anything but 1.. so 'e' should have worked.. but i guess that a mistake in the system that they forgot to put that note up.

yeah i know the derivative but i wasnt sure if thats what trips me.

tnx for help.

HallsofIvy
Homework Helper
Why are you "plugging" things in? Problem 3 asks about $a^x$, NOT $e^x$. And problem 6 has nothing to do with the value at x= 0.

i plugged in just to check if it works..
if i plug in any number but 1, it shouldnt work. since 'e' is a number too technically, it should work.

anyways, i solved the problem and i got the idea.. so problem solved :)
tnx for help!

HallsofIvy