Question

f(x)=-2sqrt{-x+4}

find f-1(x), restricting its domain so that f(x) is truly its inverse.

Answer 1

f(x)=-2sqrt{-x+4}

x must be </= 4 or f(x) will be imaginary.

x = -2 sqrt(-y+4)

x^2 = 4 (-y+4)
x^2/4 = -y + 4
y = 4 - x^2/4