For f(x)=x^2tan^-1x, find the derivative value f'(1)
f(x)=x^2tan-1x
f ' (x) = 2xtan-1x + x^2 [1/(1 + x^2)]
f ' (1) = 2pi/4 + 1 [1/2] = [pi + 1 ] / 2 ≈ 2.0708
