Slope of normal to a given function's inverse

In summary, the function f(x) = 2x2 + 4e(5x) is not invertible because it is not one-to-one. However, it is invertible in a neighborhood of x = 0. The slope of the normal line to the graph of f-1 at x = 4 is -20.
  • #1
Elixer
12
0

Homework Statement


f(x) = 2x2 + 4e(5x)
is invertible. Give the slope of the normal line to the graph of f-1 at x = 4.

Homework Equations


(Given in question)


The Attempt at a Solution


I don't know how to solve this question. But , I found the following:-

f(4) = 32 + 4e20

let y = f-1(x), then
dy/dx = 1/f ' (y)
f ' (x) = 4x + 20e(5x)
Hence, dy / dx = 1/(4y + 20e(5y))
I don't know if I am heading in the right direction.
Please help!
Thank you.
 
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  • #2
Elixer said:

Homework Statement


f(x) = 2x2 + 4e(5x)
is invertible. Give the slope of the normal line to the graph of f-1 at x = 4.

Actually,the function is not invertible because it isn't 1-1. But you might observe that f(0) = 4 and it is invertible in a neighborhood of x = 0.

Homework Equations


(Given in question)


The Attempt at a Solution


I don't know how to solve this question. But , I found the following:-

f(4) = 32 + 4e20

But f(4) isn't relevant to the question. The question is about the inverse function's slope at x = 4. Remember that f(0) = 4 means (0,4) is on the graph of y = f(x) and it also means that f-1(4) = 0 and (4,0) is on the graph of y = f-1(x).

The slope of that function at that point is what you are looking for. Does that help?
 
  • #3
LCKurtz said:
But f(4) isn't relevant to the question. The question is about the inverse function's slope at x = 4. Remember that f(0) = 4 means (0,4) is on the graph of y = f(x) and it also means that f-1(4) = 0 and (4,0) is on the graph of y = f-1(x).

The slope of that function at that point is what you are looking for. Does that help?

So, (4,0) lies on the graph of f-1(x),
y = f-1(x)
dy / dx = 1/(4y + 20e(5y))
Hence , slope of f-1(x) , dy / dx = 1/20
which implies , slope of the normal to the graph = -1 /(1/20) = -20
Ans = -20

Am I correct?
Thanks a lot!
 
  • #4
Elixer said:
So, (4,0) lies on the graph of f-1(x),
y = f-1(x)
dy / dx = 1/(4y + 20e(5y))

If you calling y = f-1(x) then I would write

y' = 1 / f'(x) = 1/(4x + 20e(5x))

and yes, your answer looks correct.
 

Related to Slope of normal to a given function's inverse

What is the slope of a normal to a given function's inverse?

The slope of a normal to a given function's inverse is the negative reciprocal of the slope of the tangent to the function's inverse at the point of intersection.

How do you find the slope of a normal to a given function's inverse?

To find the slope of a normal to a given function's inverse, first find the slope of the tangent to the function's inverse at the point of intersection. Then, take the negative reciprocal of that slope to find the slope of the normal.

What does the slope of a normal to a given function's inverse represent?

The slope of a normal to a given function's inverse represents the rate of change of the inverse function at a specific point. It also indicates the steepness of the curve of the inverse function at that point.

Can the slope of a normal to a given function's inverse be zero?

Yes, the slope of a normal to a given function's inverse can be zero if the inverse function is a horizontal line at that point. This means that the slope of the tangent to the inverse function is undefined, and therefore the negative reciprocal is also undefined.

Is the slope of a normal to a given function's inverse affected by the shape of the original function?

Yes, the slope of a normal to a given function's inverse is affected by the shape of the original function. If the original function has a steep curve at a specific point, the slope of the normal to the inverse function will also be steep at that point.

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