Hello everyone!

I'm new to this forum, I stumbled upon this domain because I really needed some help proving this equation. I'm generally horrible at this, even after practising for a bit and none of my friends are any better off than I am, so I couldn't get help anywhere.

Anyway, I need step by step proof that sinēB + sinēC -sinēA = 2cosA * sinB * sinC

If any of you could figure this out, that would be amazing.

Thanks in advance

SSG