Respuesta :

LammettHash

Since 0 < x < π/2, we know 0 < x/2 < π/4, so that cos(x/2) is still positive.

Recall the double-angle formula,

cos²(x/2) = (1 + cos(x)) / 2

so that

cos(x/2) = √((1 + 1/4) / 2) = √(5/8)