trig identities in java

I'm trying to use a formula that has sin^2(x/2) (sin squared x, not sin x squared) in it, but Math.sin^2 doesn't exist in the Math method.

Does anyone know how to express it in java?

I've found examples that give sin(x/2) or has sin(x/2)*sin(x/2)
but they don't give the correct result.

I've found one alternative, sin^2 = 1/2 - 1/2cos(2x) but that doesn't work for me either.

it's the Haversine formula for working out distance along the earths surface from to lat/long points.