1.

If 0 lt phi lt pi//2 , and x = sum_(n = 0)^(infty) cos^(2n) phi, y = sum_(n=0)^(infty) sin^(2n ) phi and z = sum_(n=0)^(infty) cos^(2n) phi sin^(2n) phi, then

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xy + z
XZ + y
x + y + z
YZ + x

Answer :A::C


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