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共回答了14个问题采纳率:85.7% 举报
(1)(a+b+c)(a-b-c)
=[a+﹙b+c﹚][a-(b+c)]
=a²-(b+c)²
=a²-(b²+2bc+c²)
=a²-b²-2bc-c²
(2) (a-2b+3c)(a+2b-3c)
=[a+(2b-3c)][a-(2b-3c)]
=a²-(2b-3c)²
=a²-4b²+9c²+10bc
2.a³+b³=(a+b)(a²-ab+b²)
a³+3ab+b³
=(a+b)(a²-ab+b²)+3ab
=(a+b)²=1
3.(3+1)(3²+1)(3²*²+1)(3²*²*²+1)(3²*²*²*²+1)
=(3-1)(3+1)(3²+1)(3²*²+1)(3²*²*²+1)(3²*²*²*²+1)/(3-1)
=(3²*²*²*²*²-1)/2
几个指数要仔细数哦!
1年前
10