Question

ok new problem i need to figure out f^-1(9) that is being plugged into the problem f(r)=pir^2 i know f^-1 means the inverse i just can't seem to get an answer for this problem

Answer 1

\(f(r) = \pi r^2\)
You understand that f(9) means plug in 9 for r in the formula above, and find the value of f, right?

Answer 2

yes i understand that much its just the inverse part that is screwing me up we having gone over much of it yet in our class

Answer 3

\(f^{-1}(r)\) means plug in the value of f and find r.
The equation you have is the formula for the area of a circle.
Just like f(9) means "what is the area of the circle with radius 9?"
\(f^{-1}\) means what is the radius for a given area.

Answer 4

ok i understand that but what would i get as a answer what i keep getting doesn't work

Answer 5

you have area=9
and you want the radius such that the area=9
That means you are to solve pi*r^2=9 for r

Answer 6

what do you get for r?

Answer 7

this is what I'm not sure of i don't understand how to bring this further

Answer 8

You want to solve for r
But you could solve for r^2 first.
Can you solve pi*r^2=9 for r^2?

Answer 9

All you need is one step to do that

Answer 10

hint: r^2 is being multiplied by pi

Answer 11

\(f(r) = \pi r^2\)

\(9 = \pi r^2\)

\(\dfrac{9}{\pi} = r^2\)

\(r = \sqrt{\dfrac{\pi}{9}}\)

\(r = \dfrac{\sqrt{\pi}}{3} \)

Answer 12

well I think @mathstudent55 gave you the recipocal of the answer

Answer 13

ok well i understand it a lot more then i did before thanks again for all your help

Answer 14

LOL. Sorry. I couldn't see as I was typing bec OS is messed up. As I type, the text goes below the screen and I have to go by what I think I'm writing.

Answer 15

I know what you mean. OS has been so annoying lately.

Answer 16

so does that mean the answer should be 3/the square root of pi?