A curve has the equation y=sin(x)cos(x), find the gradient of this curve when x = pi. (4 marks)

Option 1 - Differentiate using product rule giving dy/dx = cos²(x) - sin²(x). (2 marks) Subbing in x as pi (1 mark) then gives (-1)² + (0)² . Therefore the gradient is 1 (1 mark).  Option 2 - Initially changing sin(x)cos(x) into (sin2x)/2 (1 mark) using double angle identities, then using the chain rule to differentiate to cos(2x) (2 marks), finally subbing in x = pi for the answer of 1 (1 mark).