Question

If f(x) = 4(3x - 5), find f^-1(x)

A. f-1(x) = x+20/12
B. f-1(x) = x+5/4
C. f-1(x) = x+5/12
D. f-1(x) = x-20/12
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Answer 1

The answer is A.

Explanation:

Lets call f(x)=y, so y= 4*(3*x-5), we want to find 'x', using 'y' as a the variable.

`y=12x-20\\ y+20=12x\\ x=(y+20)/(12)`

Now lets change the name of 'y' to 'x', and 'x' to f^-1(x).

f-1(x) = (x+20)/12