Graph of f' using graphical methods

[member 731016]

Homework Statement

Please see below

Relevant Equations

Please see below

For this Problem 5,

The solution is,

However, I though the graph of f' would have end behavior more like,

Does someone please know whether I am correct?

Many thanks!

 

[Mark44]

Dose

 

[member 731016]

Thank you @Mark44, I have fixed the description now.

 

[Mark44]

Does someone please know whether I am correct?

I don't think you are correct. Why did you change the graph of f with the red dotted lines that are close to vertical?

In your altered graph of f', the parts you added look way too steep to me.

 

[member 731016]

I don't think you are correct. Why did you change the graph of f with the red dotted lines that are close to vertical?

In your altered graph of f', the parts you added look way too steep to me.

Thank you for your reply @Mark44!

Do you please agree with the solutions then?

Many thanks!

 

[Mark44]

Do you please agree with the solutions then?

Yes, pretty much. You could confirm that their graph of f' looks reasonable by tracing the graph of f on some graph paper, and then using a straight-edge at a number of points on the graph to estimate the derivative, and then plotting each of these estimates.

 

[TonyStewart]

f looks more like 4th order equation and f' looks like a 3rd order equation by counting the inflection points.

Your dotted line adds to more orders to change the direction of the asymptote of the derivative.

4. is a negative cosine function so that f' is easy to find.

 

[FactChecker]

You can expect the graph of the function to keep having more and more slopes at the extremes (negative on the left and positive on the right. Both the book answer and your answer have f' going more negative for negative x and more positive for positive x. So the next question is whether the slopes of f(x) change faster at the extremes. That is where I think the book answer is better. Notice that for x going more negative, the function has less curve and becomes straighter. That means that f' is not changing as fast (it is still becoming more negative, just slower). Likewise, on the right end, as x goes more positive, the function graph also becomes straighter. It is still sloped positively, and more positively as x gets larger, but the change is not as fast. That means that on the right side, f' keeps increasing positive, but not as fast as x gets larger.
That is why I prefer the book answer.

 

[YouAreAwesome]

Homework Statement: Please see below
Relevant Equations: Please see below

For this Problem 5,
View attachment 325718
The solution is,
View attachment 325719
However, I though the graph of f' would have end behavior more like,
View attachment 325720
Does someone please know whether I am correct?

Many thanks!

One thing that may be helpful to ponder is how the gradient, $m$, affects the line $y=mx$. When $m=1$ the line will be on a $45°$ angle. However, when the gradient is doubled to $m=2$, the angle does not double with it to $90°$, rather the angle changes to $63°$. When $m=3$, the angle is $72°$. Why does this matter? Well in the graph of $f$ we are examining the gradient of the tangents, and near the endpoints of $f$ these tangent lines are becoming closer and closer to being on the same angle. Because there is less and less increase of the gradient, the function value of $f'$ which represents the gradient, is also having less and less increase. Hence why $f'$ is flattening out.

 

[TonyStewart]

f looks more like 4th order equation and f' looks like a 3rd order equation by counting the inflection points.

Your dotted line adds to more orders to change the direction of the asymptote of the derivative.

4. is a negative cosine function so that f' is easy to find.

Furthermore in 5. (to explain why you are incorrect)

To extend f you cannot add another change in slope rather assume it is approaching a asymptotic slope so the derivative f' approaches a constant -y on the left and constant =Y on the right.

on 4. it could be a partial trig function for 1 cycle or it could also be a 4th order or more polynominal with the same shape.