Answer:
The formula for [tex]2 \sin A \cos B , 2 \cos A \sin B , 2 \sin A \sin B \text { and } 2 \cos A \sin B[/tex] are
[tex]\begin{aligned} 1 ) \sin ( A + B ) + \sin ( A - B ) & = 2 \sin A \cos B \\\\ 2 ) \sin ( A + B ) - \sin ( A - B ) & = 2 \cos A \sin B \\\\ 3 ) \cos ( A + B ) + \cos ( A - B ) & = 2 \cos A \cos B \\\\ 4 ) \cos ( A - B ) - \cos ( A + B ) & = 2 \sin A \sin B \end{aligned}[/tex]
Key points to memorise the formulas:
1. Every time try to read the formulas and write the formulas several times.
2. While learning the formulas, try to remember key points in the formulas than you can easily remember the formulas.
3. After reading the formulas try to tell somebody so that you can easily remember the formulas.
4. For cos formulas, the result will have the same trigonometric functions i.e., either sin or cos
5. For sin formulas, the result will have the different trigonometric functions i.e., both sin and cos
