Sum to product formula: sin A + sin B
sin A + sin B = 2 sin((A + B)/2) cos((A − B)/2). Going from a sum to a product is what lets you solve equations by factoring: a product is zero when either factor is, so the whole solution set falls out at once.
Related Sum to Product identities
Common questions
What is the sin A + sin B identity?
sin A + sin B = 2 sin((A + B)/2) cos((A − B)/2). Going from a sum to a product is what lets you solve equations by factoring: a product is zero when either factor is, so the whole solution set falls out at once.
Which identities are related to sin A + sin B?
sin A + sin B belongs to the Sum to Product group. The identities used alongside it most often are sin A − sin B, cos A + cos B and cos A − cos B.
Practise it
Reading a formula is not the same as recalling it under time pressure. The workspace drills Sum to Product questions in the quiz, and the triangle solver shows a worked solution for any triangle you type in.
Or browse all 45 identities in the full reference, or read the trigonometry guides for the method behind them.