A) \[2y\]
B) \[y\]
C) \[3y\]
D) None of these
Correct Answer: A
Solution :
Squaring and adding, we get \[{{x}^{2}}+{{y}^{2}}=1+1+2\,\cos \,(2A-A)\] \[\therefore \,\,\,\frac{{{x}^{2}}+{{y}^{2}}-2}{2}=\cos \,A\] ?..(i) Also \[\cos A+2\,{{\cos }^{2}}A-1=y\] or \[(\cos A+1)\,(2\,\cos A-1)=y\] Put for cos A from (i) and get the answer.
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