Question
Suppose that $A, B,$ and $C$ are the angles of a triangle, so that $A+B+C=\pi .$ Show that$\cos ^{2} A+\cos ^{2} B+\cos ^{2} C+2 \cos A \cos B \cos C=1$
Step 1
Therefore, we can express $C$ in terms of $A$ and $B$ as $C = \pi - (A + B)$. Show more…
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