# Thread: Inverses Graph #4

1. ## Inverses Graph #4

Thanks!!

Looking for a quick way to find f^-1(#) if asked to do so.

2. Originally Posted by qbkr21
Thanks!!

Looking for a quick way to find f^-1(#) if asked to do so.
remember, if $f(x) = \#$ then $f^{-1}(\#) = x$

so when they ask for, say, $f^{-1}(2)$, they are looking for the $x$ value such that $f(x) = 2$

so find a point on the graph where $y = 2$ and the corresponding $x$ value is $f^{-1}(2)$

3. ## Re:

When you mean f(x) do mean f(x) is the same thing as Y?

4. Originally Posted by qbkr21
When you mean f(x) do mean f(x) is the same thing as Y?
yes, $y = f(x)$, right?

so they ask you to find $f^{-1}(2)$, you don't know what it is, so equate it to a variable. this variable can be anything, but i chose $x$ because the answer will be an $x$-value

So let $f^{-1}(2) = x$

$\Rightarrow f \left(f^{-1}(2) \right) = f(x)$

$\Rightarrow 2 = f(x)$

So now we need to know what $x$ has to be so that $f(x)$, that is, the correspoding y-value for $x$, is 2

5. ## Re:

0

6. Originally Posted by qbkr21
0
yes

7. ## Re:

Jhevon could I just draw a horizontal line where y = #, and those spots that go through y = # would be f^-1(x)?

Thanks!!

8. Originally Posted by qbkr21
Jhevon could I just draw a horizontal line where y = #, and those spots that go through y = # would be f^-1(x)?

Thanks!!
the x-values for the points where the horizontal line cuts the graph is f^-1(#)

9. ## Re:

Would the answer to letter D be about -1.8

10. Originally Posted by qbkr21
Would the answer to letter D be about -1.8
yea, roughly -1.7,-1.8 around there. -1.8 is fine. don't think your professor will be too hard on you by being off by 0.1 since the grid is not accurate enough to be exact