g(x)=2x^2-4x-5
For g(x), write y
y = 2x^2 - 4x - 5 factor out the 2
y = 2 ( x^2 - 2x - 5/2) divide by 2
(y / 2) = x^2 - 2x - 5/2 comlplete the square on x
(y /2) = x^2 - 2x + 1 - 5/2 - 1 factor the first three terms andsimplify
(y/2) = (x - 1)^2 - 7/2 add 7/2 to both sides
[y + 7 ] / 2 = (x - 1)^2 take both roots
±√ [ ( y + 7) / 2 ] = x - 1 add 1 to both sides
±√ [ ( y + 7) / 2 ] + 1 = x swap x and y
±√ [ ( x + 7) / 2 ] + 1 = y for y, write g-1(x)
±√ [ ( x + 7) / 2 ] + 1 = g-1 (x)
So
g-1 (-2) = ±√ [ ( -2 + 7) / 2 ] + 1 = √ [5/2] + 1 or - √ [5/2] + 1