MIDTERM TOMMOROW HELP!

[hollerback1]

How do you do these problems?

Which is the inverse of the function y=-3x+12?

Find inverse of f(x) = 2x - 5

Thanks.

 

[Gene]

Swap the x & y, then solve for y.
The first one:
y=-3x+12
x=-3y+12
3y=12-x
y=(12-x)/3
That's the inverse. You can check it easily. Pick any number for x in the first one, say 4.
y=-3*4+12=0
Put x = that in the second
y=(12-0)/3 = 4.
4 is what you put in the first so the second is correct. That's what an inverse does.

 

[hollerback1]

hm...i get the flip x and y part...but the y=(12-x)/3 and y=(12-0)/3 = 4 i don't get...please reply quick THANKS :!:

 

[Unco]

I think it's dinner time in Winsconsin, so . . .

Let f(x) be the function which takes an input, x, multiplies it by -3 and adds 12, and so spits out an output, y.

The inverse function of f(x), f^-1(x), by definition, should take that output, y, and spit out the original input, x, again. To do this it must subtract 12 from y and then divide by -3.

If we input 4 to f(x), we get an output of 0.

If we plug that output of 0 into f^-1(x), we should get that original input, 4, again.

That is what Gene tested.