Question

sinc
$sinc + sind$
sin d

Answer 1

HELLO THERE!

If you are asking the formula for sin C + sin D, then here's your answer:

$sin C + sin D = 2sin\frac{C+D}{2}\times cos\frac{C - D}{2}$

The other three formulae are:

$\implies sin C - sin D = 2cos\frac{C+D}{2}\times sin\frac{C-D}{2} \\\\\\\implies cos C + cos D = 2cos\frac{C+D}{2}\times cos\frac{C-D}{2} \\\\\\\implies cos C - cos D = 2sin\frac{C + D}{2}\times sin\frac{D-C}{2}$

These formulae are called as "Transformation Formulae", as the sum of two trigonometric quantities are converted to product form.

THANKS!