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If sin A+sin B=a and cos A+cos B=b then ...

If `sin A+sin B=a` and `cos A+cos B=b` then `cos (A+B)=`

A

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

B

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

C

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

D

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

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