JEE PYQ: Binomial Theorem Question 30
Question 30 - 2020 (07 Jan Shift 1)
If the sum of the coefficients of all even powers of $x$ in the product $(1 + x + x^2 + \ldots + x^{2n})(1 - x + x^2 - x^3 + \ldots + x^{2n})$ is 61, then $n$ is equal to ____.
Show Answer
Answer: 30
Solution
Put $x = 1$ and $x = -1$: $2n + 1 = 61$, $n = 30$.