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Question
The coefficient of x8 y10 in the expansion of (x + y)18 is
Options
18C8
18p10
218
none of these
Solution
18C8
\[\text{ Suppose the (r + 1)th term in the given expansion contains } x^8 y^{10} . \]
\[\text{ Then, we have } \]
\[ T_{r + 1} =^{18}{}{C}_r x^{18 - r} y^r \]
\[\text{ For the coefficient of } x^8 y^{10} \text{ We have} \]
\[r = 10\]
\[\text{ Hence, the required coefficient is }^{18}{}{C}_{10} \text{ or } ^{18}{}{C}_8\]
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