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

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

A

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

B

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

C

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

D

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

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The correct Answer is:

B

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