Question

prove that cos75-cos15= -1/root 2

Answer 1

we have formula cosA-cosB =2sin(A+B)/2 *sin(B-A)/2

using formula,

2 * sin(90/2)*sin(60/2) = 2 * sin45 * sin30

2 * 1/root(2)*1/2

= 1/root2

hence proved