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If cosalpha+cosbeta=a ,sinalpha+sinbeta=...

If `cosalpha+cosbeta=a ,sinalpha+sinbeta=b and alpha-beta=2theta,` then `(cos3theta)/(costheta)=`

A

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

B

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

C

`3-a^(2) - 3`

D

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

Text Solution

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The correct Answer is:
B
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