# If Sin a + Sin B = α and Cos a + Cos B = β, Then Write the Value of Tan ( a + B 2 ) . - Mathematics

Sum

If sin A + sin B = α and cos A + cos B = β, then write the value of tan $\left( \frac{A + B}{2} \right)$.

#### Solution

Given:
sin A + sin B = α            .....(i)
cos A + cos B = β           .....(ii)
Dividing (i) by (ii):

$\Rightarrow \frac{\sin A + \sin B}{\cos A + \cos B} = \frac{\alpha}{\beta}$

$\Rightarrow \frac{2\sin\left( \frac{A + B}{2} \right)\cos\left( \frac{A - B}{2} \right)}{2\cos\left( \frac{A + B}{2} \right)\cos\left( \frac{A - B}{2} \right)} = \frac{\alpha}{\beta} \left[ \because \sin A + \sin B = 2\sin\left( \frac{A + B}{2} \right)\cos\left( \frac{A - B}{2} \right)\text{ and }\cos A + \cos B = 2\cos\left( \frac{A + B}{2} \right)\cos\left( \frac{A - B}{2} \right) \right]$

$\Rightarrow \frac{\sin\left( \frac{A + B}{2} \right)\cos\left( \frac{A - B}{2} \right)}{\cos\left( \frac{A + B}{2} \right)\cos\left( \frac{A - B}{2} \right)} = \frac{\alpha}{\beta}$

$\Rightarrow \tan\left( \frac{A + B}{2} \right)=\frac{\alpha}{\beta}$

Concept: Transformation Formulae
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#### APPEARS IN

RD Sharma Class 11 Mathematics Textbook
Chapter 8 Transformation formulae
Q 3 | Page 20