Show that cos2A + cos2B - 2cos Acos Bcos (A+B) = sin2(A+B) .

Show that $\cos^{2} A + \cos^{2} B - 2 \cos A \cos B \cos (A + B) = \sin^{2} (A + B)$ .

Put the parts in order to form a sentence. When you think your answer is correct, click on "Check" to check your answer. If you get stuck, click on "Hint" to find out the next correct part.