Question

f(x) = cos(x)
f'(x) = -sin(x)
f'(π/2) = -sin(π/2)
f'(π/2) = -1

My answer to this question is A. -1, but I am posting it here because several students got B. +1 as their answer. Can anyone confirm the answer as A?

Answer 1

Your working out is correct. The appropriate answer is ...
  A. -1

For confirmation, check a graph of cos(x) at π/2. It has negative slope at that point.

Answer 2

Your answer would be -1.