Use the product-to-sum formula to write the given product as a sum or difference.

6sin π/10 cos π/ 10

4 answers

look up your formulas. You want

2 sin(a) cos(b) = sin(a+b) cos(a-b)

You don't even need the product-to-sum formulas, since your double-angle formula says that

cos(2x) = 2 sinx cosx
Dang! That is

sin(2x) = 2 sinx cosx
that isn't one of my answers?
you telling me or asking me?

Naturally, sin(2x) is not one of your answers, but if you let x = π/10 and you plug that in, I bet it is one of your answers.