Question

Let f(x) = x2 - 81. Find f-1(x).

±square root of the quantity x plus 81

9square root of x

1 over quantity x squared minus 81

x squared over 81

Answer 1

To find the inverse:

Replace f(x) with y
Switch x's and y's, so put x where y is and x where y is.
Solve for y
Replace y with f^-1(x)

Answer 2

yea i did that but i got confused

Answer 3

I've seen you attempt harder problems, show me where you went wrong :P

Answer 4

this is where i stop at

y=5x+12
x=5y+12
x-12/5=5y/5
x-12/5=fx

Answer 5

Wrong problem? y =5x+12?

Answer 6

opps wrong one i got the answer to that one i mean i really didn't start the question i am asking you

Answer 7

Lol well, follow the steps I gave you, and we can see how you do :)

Answer 8

\[f(x) = x^-81 \implies y = x^2-81\]

Answer 9

Do the next step :D

Answer 10

is it C

Answer 11

Jagr I don't understand, it's just simple algebra, I've seen you answer much tougher questions..mhm, and no actually do the problem instead of guessing. Just follow the steps I gave you, I'll help you.

Answer 12

So we have y=x^2-81, next step?

Answer 13

x-81=y^2

Answer 14

No, that's not right, you just replaced the square from x to y, not the variable itself.

Answer 15

THIS is CONFUSING. ok so was i even close

Answer 16

\[y=x^2-81, ~~~ x=y^2-81\] that's all you had to do, don't over complicate it.

Answer 17

oh ok

Answer 18

Now solve for y

Answer 19

x squared over 81

Answer 20

do you square root 81 to 9

Answer 21

\[y = \pm \sqrt{x+81}\]

Answer 22

Now just change the y back to f^(-1)

Answer 23

so its A

Answer 24

@iambatman is it A

Answer 25

Yes it is A.