Q. 75.0( 1 Vote )
Prove that:
Answer :
By regrouping the LHS and multiplying and dividing by 4 we get,
But 2sin A sin B = cos (A–B) –cos (A+B)
Then the above equation becomes,
But cos(90°–θ)=sin θ and cos(180°–θ)=–cos(θ).
Then the above equation becomes,
Now, 
Substituting the corresponding values, we get
Hence proved
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