Math-trig question

Question

Reduce sin 40° cos 40° to a single function of one angle.

a. cos 80°

b. 1/2 sin 80°

c. sin 80°

c. 1/2 cos 80°

Answer 1

sin/cos=tan

cos/sin=cot

Answer 2

Recall that sin(2A) = 2sinAcosA

So, sinAcosA = (1/2)sin(2A)

Therefore, sin40ˆcos40ˆ = (1/2)sin80ˆ