赋值法求二项式系数和
例1.若,则
(1)_________;
(2)_________;
(3)_________;
(4)_________;
(5)_________;
(6)_________;
(7)_________;
(8)_________;
(9)_________;
(10)_________;
(11)_________.
解析:(1)令,则;
(2)令,则,
故;
(3)由(1)(2)知;
(4);
(5)平方差公式,
(6)令,则;
(7)令,则;
(8)对原式求导,,令,则;
(9)对原式求导,,令,则;
(10)原式可由求导得到,令,则;
(11)原式可由求导得到,令,则
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