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JEE Main 20268 AprilEvening Shift
Exam
JEE Main
Year
2026
Date
8 April
Shift
Evening Shift
Subject
Mathematics
Chapter
Functions

JEE Main 2026 · 8 April · Evening Shift · Mathematics · Functions

Let f be a polynomial function such that _2(f(x)) = (...

Let ff be a polynomial function such that log⁡2(f(x))=(log⁡2(2+23+29+…∞))⋅log⁡3(1+f(x)f(1/x))\log_2(f(x)) = \left(\log_2\left(2+\dfrac{2}{3}+\dfrac{2}{9}+\ldots\infty\right)\right)\cdot\log_3\left(1+\dfrac{f(x)}{f(1/x)}\right), x>0x>0 and f(6)=37f(6)=37. Then ∑n=110f(n)\displaystyle\sum_{n=1}^{10}f(n) is equal to ________.

Correct answer

0

Step-by-step solution

The sum of the infinite geometric progression is given by:

S=2+23+29+…∞=21−13=3S = 2 + \dfrac{2}{3} + \dfrac{2}{9} + \ldots \infty = \dfrac{2}{1 - \dfrac{1}{3}} = 3

Substituting this into the given equation:

log⁡2(f(x))=log⁡2(3)⋅log⁡3(1+f(x)f(1/x))\log_2(f(x)) = \log_2(3) \cdot \log_3\left(1 + \dfrac{f(x)}{f(1/x)}\right)

Using the base change property log⁡a(b)⋅log⁡b(c)=log⁡a(c)\log_a(b) \cdot \log_b(c) = \log_a(c):

log⁡2(f(x))=log⁡2(1+f(x)f(1/x))\log_2(f(x)) = \log_2\left(1 + \dfrac{f(x)}{f(1/x)}\right)

Equating the arguments:

f(x)=1+f(x)f(1/x)f(x) = 1 + \dfrac{f(x)}{f(1/x)}

f(x)f(1/x)−f(1/x)=f(x)f(x)f(1/x) - f(1/x) = f(x)

f(x)f(1/x)=f(x)+f(1/x)f(x)f(1/x) = f(x) + f(1/x)

The only polynomial functions satisfying this relation are of the form f(x)=1±xnf(x) = 1 \pm x^n.

Given f(6)=37f(6) = 37:

1±6n=371 \pm 6^n = 37

Taking the positive sign, 6n=36⇒n=26^n = 36 \Rightarrow n = 2.

Thus, the polynomial is f(x)=x2+1f(x) = x^2 + 1.

The required sum is:

∑n=110f(n)=∑n=110(n2+1)\sum_{n=1}^{10} f(n) = \sum_{n=1}^{10} (n^2 + 1)

∑n=110f(n)=∑n=110n2+∑n=1101\sum_{n=1}^{10} f(n) = \sum_{n=1}^{10} n^2 + \sum_{n=1}^{10} 1

∑n=110f(n)=10×11×216+10\sum_{n=1}^{10} f(n) = \dfrac{10 \times 11 \times 21}{6} + 10

∑n=110f(n)=385+10=395\sum_{n=1}^{10} f(n) = 385 + 10 = 395

Answer: 395395
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