Jumlah dan Selisih Trigonometri

\sin(A+B)=\sin A\cos B+\cos A\sin B
\sin(A-B)=\sin A\cos B-\cos A\sin B
\cos(A+B)=\cos A\cos B+\sin A\sin B
\cos(A-B)=\cos A\cos B-\sin A\sin B

\sin A+\sin B=2\sin\left(\dfrac{A+B}2\right)\cos\left(\dfrac{A-B}2\right)
\sin A-\sin B=2\cos\left(\dfrac{A+B}2\right)\sin\left(\dfrac{A-B}2\right)
\cos A+\cos B=2\cos\left(\dfrac{A+B}2\right)\cos\left(\dfrac{A-B}2\right)
\cos A-\cos B=-2\sin\left(\dfrac{A+B}2\right)\sin\left(\dfrac{A-B}2\right)