(a+b+c)*2a*3+b*3(a+b)*3(a-b)*3
注:“*”是乘号!
1.2a+2b+2c
2.3(a+b)
3.3a+3b
4.3a-3b
(a+b+c)²=a²+b²+c²+2ab+2bc+2ca
a³+b³=(a+b)(a²-ab+b²)
(a+b)*3=a³+3a²b+3ab²+b³ (a-b)*3=a³-3a²b+3ab²-b³