What is the coeﬃcient of $$x ^ { 2 } y ^ { 7 } \text { in } ( x + y ) ^ { 9 } ?$$

Name: What is the coeﬃcient of \[x ^ { 2 } y ^ { 7 } \text { in } ( x + y ) ^ { 9 } ?\]
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ext { By the binomial theorem the coefficient of } x ^ { 2 } y ^ { 7 } ext { in } ( x + y ) ^ { 9 } ext { is } \left( \begin{array} { l } 9 \2\end{array} ight) = \frac { 9 ! } { 7 ! 2 ! } = \frac { 9 \cdot 8 } { 2 \cdot 1 } = 36 ext {. }

What Is the Coeﬃcient Of x2y7 in (x+y)9?x ^ { 2 } y ^ { 7 } \text { in } ( x + y ) ^ { 9 } ?x2y7 in (x+y)9?