Question

What are the compound angle formulae?

Answer 1

Compound angle formulae
\[
\begin{array}{ll}
\cos (A-B)=\cos A \cdot \cos B+\sin A \cdot \sin B & \cos (A+B)=\cos A \cdot \cos B-\sin A \cdot \sin B \\
\sin (A-B)=\sin A \cdot \cos B-\cos A \cdot \sin B & \sin (A+B)=\sin A \cdot \cos B+\cos A \cdot \sin B
\end{array}
\]
Double angle formulae
\[
\sin 2 \mathrm{~A}=2 \sin \mathrm{A} \cdot \cos \mathrm{A} \quad \cos 2 \mathrm{~A}=\left\{\begin{array}{l}
\cos ^2 \mathrm{~A}-\sin ^2 \mathrm{~A} \\
2 \cos ^2 \mathrm{~A}-1 \\
1-2 \sin ^2 \mathrm{~A}
\end{array}\right.
\]