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Mathematics · 2020
JEE Main · 7 January 2020, Shift 1 · Q72
If the sum of the coefficients of all even powers of x in the product (1+x+x^2+…+x^2 n)(1-x+x^2-x^3+…+x^2 n) is 61, then n is equal to \ \ \ \.
If the sum of the coefficients of all even powers of $\displaystyle x$ in the product
$$\left(1+x+x^2+\ldots+x^{2 n}\right)\left(1-x+x^2-x^3+\ldots+x^{2 n}\right)
$$
is $\displaystyle 61$, then n is equal to \_\_\_\_.
Official answer
30
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JEE Main 2020 Mathematics question, with the answer from NTA’s final answer key. Where our answers come from.