1.

If `x+y=z`, then `cos^(2)x+cos^(2)y+cos^(2)z-2cosx.cosy.cosz` is equal toA. `cos^(2)z`B. `sin^(2)z`C. 0D. 1

Answer» Correct Answer - D
`cos^(2)x+cos^(2)y+cos^(2)z-cosz(cos(x+y)+cos(x-y))`
`=cos^(2)x+cos^(2)y+cos^(2)z-cos^(2)z-cos(x+y).cos(x-y)=1`


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