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Question

Question: If y = (1 + x) (1 + x<sup>2</sup>) (1 + x<sup>4</sup>) …. (1 + x<sup>2n</sup>), then \(\frac{dy}{dx}...

If y = (1 + x) (1 + x2) (1 + x4) …. (1 + x2n), then dydx\frac{dy}{dx} at x = 0 is

A

1

B

– 1

C

0

D

None of these

Answer

1

Explanation

Solution

y = (1x)(1x)\frac{(1 - x)}{(1 - x)} (1 + x2)….(1 + x2n) = 1(x2n)21x\frac{1 - (x^{2n})^{2}}{1 - x}

dydx=(1x)(04n4n1)(1x2n)(1)(1x)2\frac{dy}{dx} = \frac{(1 - x)(0 - 4n^{4n - 1}) - (1 - x^{2n})( - 1)}{(1 - x)^{2}} ; at x = 0 ⇒ 1