解ï¼
(1+x)Ã(1-x)^6
=(1+x)[...+ax³+bx²+...]
=...+ax³+bx³+...
=....+(a+b)x³+.....
â´åªè¦æ±å¾(1-x)^6çå±å¼å¼ä¸çx²ä¸x³è¿ä¸¤é¡¹çç³»æ°å³å¯ã
ï¼1-x)^6çé项ï¼T(1+r)=C(6,r)Ã(-x)^r
å½r=3æ¶ï¼T(4)=C(6,3)Ã(-x)³=-20x³=ax³. a=-20
å½r=2æ¶ï¼T(3)=C(6,2)Ãx²=15x²=bx², b=15
â´è¦æ±çx³çç³»æ°ä¸ºa+b=-5
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