a) f'(x) =-1/(x-1)²
f'(2)=-1/1=-1
b) f(x) =(lnx-1+1)/(lnx-1)=1+1/(lnx-1)
f'(x)=-1/(lnx-1)² *(1/x)
f'(e²)= -1/1 * (1/e²) =-1/e²
c) f(x) =cosx/(2+sinx)
f'(x) =(-sinx(2+sinx)-cosx*cosx)/(2+sinx)²= (-2sinx-1)(2+sinx)²= -(2sinx+1)/(2+sinx)²
f'(π/2)=-(2+1)(2+1) =-3/3=-1