A-3. Ifx = y cos Z COS then xy + y2...
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A-3. Ifx = y cos Z COS then xy + y2 + zx is equal to (B) 0 (C) 1 (A) - 1 (D) 2

JEE/Engineering Exams
Maths
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( begin{aligned} x &=y cos frac{2 pi}{3}=frac{3 cos 4 pi}{3} x &=y cos left(pi-frac{pi}{3}right)=3 cos left(pi frac{pi}{3}right) x &=-y cos frac{pi}{3}=-3 cos pi / 3 x &=frac{-y}{2}=frac{-3}{2} Rightarrow & y=-2 x=3 end{aligned} ) ( begin{array}{rl}x y+y z+z & x=y x(-2 x)+(-2 x)(-2 x)+(-2 x) x & =-2 x^{6}+4 x^{2}-2 x^{2} & =0end{array} )
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