InterviewSolution
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InterviewSolution
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If `cos x+cos y-cos(x+y)=(3)/(2)`, thenA. `x+y=0`B. x=2yC. x=yD. 2x=y |
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Answer» Correct Answer - B `cos x+cosy-cos(x+y)=(3)/(2)` or `2cos((x+y)/(2))cos((x-y)/(2))-2cos^(2)((x+y)/(2))+1=(3)/(2)` or `2cos^(2)((x+y)/(2))-2cos((x+y)/(2))cos((x-y)/(2))+(1)/(2)=0`. Now `cos((x+y)/(2))` is always real, then discriminant `ge0`. Thus, `4cos^(2)((x-y)/(2))-4ge0` or `cos^(2)((x-y)/(2))ge1` or `cos^(2)((x-y)/(2))=1` or `(x-y)/(2))=0` or x=y. |
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