how to solve this function...

Question

if f(x)=4x-x^2 find f(x+h)-f(x-h)/2h

Answer 1

f(x) =4x - x²

[f(x+h) - f(x-h)] / (2h) = [4(x+h) - (x+h)² - 4(x-h) + (x-h)²] / (2h)

= [4x + 4h - x² - 2xh - h² - 4x + 4h + x² - 2xh + h²] / (2h)

= [8h - 4xh] / (2h)

= 4 - 2x