If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Proof: sin(a+b) = (cos a)(sin b) + (sin a)(cos b)

Proof of the trig identity sin(a+b) = (cos a)(sin b) + (sin a)(cos b)