f(x) = 4x - x^2
1)
f(4) = 4(4) - 4^2 = 16 - 16 = 0
f(-4) = 4(-4) - (-4)^2 = -16 - 16 = -32
f(4) - f(-4) = 0 - (-32) = 32
2)
f(3/2) = 4(3/2) - (3/2)^2
f(3/2) = 6 - 9/4 = 15/4
√f(3/2) = √(15/4) = √15 / 2
3)
f(x + h) = 4(x + h) - (x + h)^2
= 4x + 4h -(x^2 + 2xh + h^2)
= 4x + 4h -x^2 - 2xh - h^2
f(x - h) = 4(x - h) - (x - h)^2
= 4x - 4h -(x^2 - 2xh + h^2)
= 4x - 4h -x^2 + 2xh - h^2
So
[f(x + h) -f(x - h) ] / 2h
= [4x + 4h -x^2 - 2xh - h^2 - ( 4x - 4h -x^2 + 2xh - h^2 )] / 2h
=( 4x + 4h -x^2 - 2xh - h^2 - 4x + 4h + x^2 - 2xh + h^2 ) / 2h
= (8h - 4xh) / 2h
= 2h(4 -2x) / 2h
= 4 - 2x
Answer: [f(x + h) -f(x - h) ] / 2h = 4 - 2x