杨辉三角的减法计算(a-b)^7=?

(a-b)^7=
a^7-7a^6b+21a^5b^2-35a^4b^3+35a^3b^4-21a^2b^5+7ab^6-b^7

1
1,1
1,2,1
1,3,3,1
1,4,6,4,1
1,5,10,10,5,1
1,6,15,20,15,6,1
1,7,21,35,35,21,7,1
(a-b)^7=a^7-7a^6b+21a^5b²-35a^4b³+35a³b^4-21a²b^5+7ab^6-b^7
把-b看成整体即可，展开b的奇次方前为负号

a^7-7a^6b+21a^5b^2-35a^4b^3+35a^3b^4-21a^2b^5+7ab^6-b^7