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If cos alpha+ cos beta= a, sin alpha+ si...

If `cos alpha+ cos beta= a, sin alpha+ sin beta= b and alpha- beta= 2 theta`. Then `(cos 3 theta)/(cos theta)=`

A

`3 - a ^(2) - b ^(2)`

B

`(a ^(2) + b ^(2))/(4)`

C

`a ^(2) + b ^(2) -1`

D

`a ^(2) + b ^(2) -3 `

Text Solution

Verified by Experts

The correct Answer is:
D
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