JEE MAIN PYQ
1
$ \left( \frac{1}{3} + \frac{4}{7} \right) + \left( \frac{1}{3^2} + \frac{1}{3} \times \frac{4}{7} + \frac{4^2}{7^2} \right) + \left( \frac{1}{3^3} + \frac{1}{3^2} \times \frac{4}{7} + \frac{1}{3} \times \frac{4^2}{7^2} + \frac{4^3}{7^3} \right) + \ldots \text{ upto infinite terms is equal to }$
Go to Discussion
JEE MAIN JEE Mains PYQ
JEE MAIN JEE Main 2026 (24 January Evening Shift) PYQ
Solution
Let $ a = \frac{4}{7},; b = \frac{1}{3} $
Multiply $ N $ and $ D $ by $ (a - b) = \frac{4}{7} - \frac{1}{3} = \frac{5}{21} $
$ \frac{1}{a - b} \left[ (a^2 - b^2) + (a^3 - b^3) + (a^4 - b^4) + \ldots \right] $
$ = \frac{1}{a - b} \left[ \frac{a^2}{1 - a} - \frac{b^2}{1 - b} \right] $
$ = \frac{21}{5} \left[ \frac{16/49}{1 - 4/7} - \frac{1/9}{1 - 1/3} \right] $
$ = \frac{21}{5} \left[ \frac{16/49}{3/7} - \frac{1/9}{2/3} \right] $
$ = \frac{21}{5} \left[ \frac{16}{21} - \frac{1}{6} \right] $
$ = \frac{21}{5} \cdot \frac{96 - 21}{126} $
$ = \frac{21}{5} \cdot \frac{75}{126} $
$ = \frac{15}{6} = \frac{5}{2} $
JEE MAIN PYQ
2
The value of $ \sum_{k=1}^{\infty} (-1)^{k+1} \frac{k(k+1)}{k!} $ is:
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JEE MAIN JEE Mains PYQ
JEE MAIN JEE Main 2026 (28 January Morning Shift) PYQ
Solution
$ T_k = (-1)^{k+1} \frac{k(k+1)}{k!} = (-1)^{k+1} \frac{k(k-1) + 2k}{k!} $
$ = (-1)^{k+1} \left[ \frac{k(k-1)}{k!} + \frac{2k}{k!} \right] $
$ = (-1)^{k+1} \left[ \frac{1}{(k-2)!} + \frac{2}{(k-1)!} \right] $
$ \Rightarrow \sum = \sum_{k=1}^{\infty} (-1)^{k+1} \frac{1}{(k-2)!} + 2 \sum_{k=1}^{\infty} (-1)^{k+1} \frac{1}{(k-1)!} $
$ = \sum_{k=0}^{\infty} \frac{(-1)^k}{k!} = \frac{1}{e} $
JEE MAIN PYQ
2
$ \frac{6}{3^{26}} + \frac{10.1}{3^{25}} + \frac{10.2}{3^{24}} + \frac{10.2^2}{3^{23}} + \ldots + \frac{10.2^{24}}{3} $ is equal to
Go to Discussion
JEE MAIN JEE Mains PYQ
JEE MAIN JEE Main 2026 (28 January Evening Shift) PYQ
Solution
$ S = \frac{6}{3^{26}} + \frac{10}{3^{25}}\left[ \frac{(6)^{25} - 1}{6 - 1} \right] $
$ S = \frac{6}{3^{26}} + \frac{10}{3^{25}} \cdot \frac{6^{25} - 1}{5} $
$ S = \frac{2}{3^{25}} + 2\left[ 2^{25} - \frac{1}{3^{25}} \right] $
$ S = 2^{26} $
JEE MAIN PYQ
2
$ \sum_{r=1}^{25} \frac{r}{r^2 + r + 1} = \frac{p}{q} $, where $ p $ and $ q $ are integers such that $ \gcd(p, q) = 1 $, then $ p + q $ is equal to
Go to Discussion
JEE MAIN JEE Mains PYQ
JEE MAIN JEE Main 2026 (28 January Evening Shift) PYQ
Solution
$ S = \sum \frac{r}{(r^2 + r + 1)} $
$ = \frac{1}{2} \sum \left( \frac{1}{r^2 - r + 1} - \frac{1}{r^2 + r + 1} \right) $
$ = \frac{1}{2} \left[ \left(1 - \frac{1}{3}\right) + \left(\frac{1}{3} - \frac{1}{7}\right) + \ldots + \left(\frac{1}{601} - \frac{1}{651}\right) \right] $
$ = \frac{1}{2}\left(1 - \frac{1}{651}\right) = \frac{325}{651} $
$ \Rightarrow p = 325,; q = 651 \Rightarrow p + q = 976 $
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