If the co-efficient of x7 and x8 in the expansion of ${\left( {2 + {x \over 3}} \right)^n}$ are equal, then the value of n is equal to _____________.
Answer (integer)
55
Solution
${}^n{C_7}{2^{n - 7}}{1 \over {{3^7}}} = {}^n{C_8}{2^{n - 8}}{1 \over {{3^8}}}$<br><br>$\Rightarrow$ n $-$ 7 = 48 $\Rightarrow$ n = 55
About this question
Subject: Mathematics · Chapter: Binomial Theorem · Topic: Binomial Expansion
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