1.

If `x =cos alpha+cos beta-cos(alpha+beta)` and `y=4 sin.(alpha)/(2)sin.(beta)/(2)cos.((alpha+beta)/(2))`, then (x-y) equals

Answer» Correct Answer - A
`y=4 sin.(alpha)/(2)sin.(beta)/(2)cos((alpha+beta)/(2))`
`=2[cos.(alpha-beta)/(2)-cos.(alpha+beta)/(2)]cos((alpha+beta)/(2))`
`= cos alpha + cos beta - (1+cos (alpha + beta))=x-1`
`rArr x-y=1`
`cos 5^(@)cos 20^(@)+cos 35^(@)cos 50^(@)`


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