Question

Is Cos(A+B) cosA+cosB. Justify ​

Answer 1

Yes cause the term which is outsider having a bracket equation that term will be multiplied by the whole braket equation
So,
Cos(A+B)=
Cos multiple A=CosA +
Cos multiple B=Cos B
Hence,
cosA+CosB is correct

Answer 2

$\cos(A + B) \cancel{ = } \cos(A) + \cos( B)$

Use any values for checking this .

Example let :- A= 45 and B = 30

$\cos(45 + 60) \cancel= \cos(45) + \cos(60) \\ \cos(105) \cancel= \frac{1}{ \sqrt{2} } + \frac{1}{2} \\ - 0.2 \cancel= 0.7 + 0.5 \\ \\ - 0.2 \cancel = 1.2$