# Trigonometry #01

Algebra Level pending

For $$0<\phi \le \cfrac { \pi }{ 2 }$$ , if $$x=\sum _{ n=0 }^{ \infty }{ { cos }^{ 2n } } \phi$$ , $$y=\sum _{ n=0 }^{ \infty }{ { sin }^{ 2n } } \phi$$ , $$z=\sum _{ n=0 }^{ \infty }{ { { cos }^{ 2n }\phi .sin }^{ 2n } } \phi$$ , then

Source : IIT JEE, 1992

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