1.

यदि `cosx,cosy+sinx.siny=-1` हो तो `cosx+cosy` का मान होगा ?A. -2B. 1C. 0D. 2

Answer» Correct Answer - c
` cosx.cosy+sinx.siny=-1`
`cosx=y=-1`
`cos(x-y)=cos180^(@)`
`x -y=180^(@)`
`x- y=180^(@)`
`cosx+cosy=2cos(x+y)/(2).cos`
`(x-y)/(2)`
`=2cos(x+y)/(2).cos(180)/(2)`
`=2cos(x+y)/(2)cos90^(@)`
`cos90^(@)=0`
`cos x+cosy=0`


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