Trigonometric Identities Question 371
Question: If $ \cos (A+B)=\alpha \cos A\cos B+\beta \sin A\sin B, $ then $ (\alpha ,\beta ) $ =
[MP PET 1992]
Options:
A) (-1, -1)
B) (- 1, 1)
C) (1, -1)
D) (1, 1)
Show Answer
Answer:
Correct Answer: C
Solution:
Given $ \cos ,(A+B)=\alpha ,\cos A,\cos B+\beta ,\sin A,\sin B $ But $ \cos ,(A+B)=\cos ,A,\cos B-\sin A,\sin ,B $
$ \Rightarrow \alpha =1,\beta =-1. $
BETA
