InterviewSolution
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InterviewSolution
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If `cos (x-y),, cosx and cos(x+y)` are in H.P., are in H.P., then `cosx*sec(y/2)`=A. `pmsqrt(2)`B. `(1)/(sqrt(2))`C. `-(1)/(sqrt(2))`D. None of these |
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Answer» Correct Answer - A `:.cos(x-y),cosx,cos(x+y)` are in HP. `:.cosx=(2cos(x-y)cos(x+y))/(cos(x-y)+cos(x+y))` `implies cosx=(2cos^(2)x-sin^(2)y)/(2cosx cosy)` `implies cos^(2)x cosy =cos^(2)x-sin^(2)y` `implies cos^(2)x(1-cosy)=sin^(2)y` `=(1+cos y)(1-cosy )` `implies cos^(2)x=(1+cosy)" "[:.1-cosyne0]` `implies cos^(2)x= 2 cos^(2)""(y)/(2)` `implies cos^(2)xsec^(2)((y)/(2))=2` `:. cos x sec ((y)/(2))= pm sqrt(2)` |
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