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Basics & Logarithms: Value Expression

JEE Maths question with a full step-by-step solution.

Question
If x=n=12026nx = \prod_{n=1}^{2026} n, then the value of the expression
11log2x+1log3x++1log2026x\frac{1}{\dfrac{1}{\log_2 x} + \dfrac{1}{\log_3 x} + \cdots + \dfrac{1}{\log_{2026} x}}
is
Solution
Answer: 1
Step 1: Convert each term using the change-of-base identity.
1logkx=logxk\frac{1}{\log_k x} = \log_x k
So the denominator becomes:
logx2+logx3++logx2026=logx(232026)\log_x 2 + \log_x 3 + \cdots + \log_x 2026 = \log_x(2 \cdot 3 \cdots 2026)
Step 2: Since x=1232026x = 1 \cdot 2 \cdot 3 \cdots 2026, we have 232026=x2 \cdot 3 \cdots 2026 = x. Therefore the denominator equals logxx=1\log_x x = 1. Step 3: The entire expression equals 11=1\dfrac{1}{1} = 1. Answer: 1
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