f(x) = sin x + cos x/sin x, tentukan f' (π/4) ?

f(x) = sin x + cot x
f'(x) = cos x - cosec^2 x
f'(π/4) = cos π/4 - cosec^2 π/4
= 1/2 √2 - (2/√2)^2
= 1/2 √2 - 4/2 
= (√2-4)/2