Question

Evaluate sin square 72 - sin square 60

Answer 1

Answer:

sin^2 72 - sin^2 60

= ( sin72 + sin60) ( sin72- sin60)

=2 sin(72+60)/2 cos ( 72-60)/2 * 2cos(72+60)/2 sin(72-60)/2

= sin132* sin12= .1545

again ( sqrt5-1)/8 = . 1545