SOLUTION: Suppose f(x)=(x/8)-3 and g(x)=x^3. Find (f o g)^-1(x)

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Question 998705: Suppose f(x)=(x/8)-3 and g(x)=x^3. Find (f o g)^-1(x)
Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!
Suppose f(x)=(x/8)-3 and g(x)=x^3. Find (f o g)^-1(x)
First we find fog(x) by substituting the right side of
g(x) for x in f(x):

fog%28x%29%22%22=%22%22x%5E3%2F8-3

fog%28x%29%22%22=%22%22x%5E3%2F8-24%2F8

fog%28x%29%22%22=%22%22%28x%5E3-24%29%2F8

Now we find the inverse of fog(x), or fog-1(x):

Substitute y for fog(x)

y%22%22=%22%22%28x%5E3-24%29%2F8

Swap x and y

x%22%22=%22%22%28y%5E3-24%29%2F8

Solve for y.

Multiply both sides by 8

8x%22%22=%22%22y%5E3-24

Add 24 to both sides:

8x%2B24%22%22=%22%22y%5E3

y%5E3%22%22=%22%228x%2B24

Take cube roots of both sides:

y%22%22=%22%22root%283%2C8x%2B24%29

Replace y by fog-1(x)

fog-1(x)%22%22=%22%22root%283%2C8x%2B24%29

Edwin