# Cos + cos b

You noticed that the equation c 2 = a 2 + b 2 – 2bc cos (C) resembles the Pythagorean Theorem, except for the last terms,” – 2bc cos (C).” For this reason, we can say that the Pythagorean Theorem is a special of the sine rule.

Recall also the following trigonometric identities: sin(x±y)=sinxcosy±cosxsiny. Click here to get an answer to your question ✍️ Given cos (A - B) = cos A cos B + sin A sin B . Taking suitable A and B , find cos 15^∘ . 23 Jul 2019 cos(A-B) = cosAcosB+sinAsinB.