展开式：(a+b)^6(a-b)^5(a+2b)^4贾宪（杨辉）三角.写出上面三个式子的展开式：如：（a+b）^4=a^4+4a^3b+6a^2b^2+4ab^3+b^4

Question

展开式：(a+b)^6 (a-b)^5 (a+2b)^4
贾宪（杨辉）三角.
写出上面三个式子的展开式：
如：（a+b）^4=a^4+4a^3b+6a^2b^2+4ab^3+b^4

Answer 1

(a+b)^6=a^6+6a^5b+15a^4b^2+20a^2b^3+15a^2b^4+6ab^5+b^6
(a-b)^5=a^5-5a^4b+10a^3b^2-10a^2b^3+5ab^4-b^5
(a+2b)^4=a^4+8a^3b+24a^2b^2+32ab^3+16b^4