If x= _ n=a ^ (-1)^ n ^ 2 n and y= _ n=a ^ ^ 2 n , for 0< < 4 , then :
Mathematics · JEE Main · NTA Exams — Progression and Series
If \(x=\sum_{n=a}^{\infty}(-1)^{n} \tan ^{2 n} \theta \text { and } y=\sum_{n=a}^{\infty} \cos ^{2 n} \theta, \text { for } 0<\theta<\frac{\pi}{4}\), then :
- y(1 - x) = 1
- y(1 + x) = 1
- x(1 + y) = 1
- x(1 - y) = 1
Answer
(B) y(1 + x) = 1
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