(a-b)^5
=(a^5)-5(a^4)b+10a³b²-10a²b³+5a(b^4)-(b^5)
(a+2b)^4
=(a^4)+4a³(2b)+6a²(2b)²+4a(2b)³+(2b)^4
=(a^4)+8a³b+24a²b²+32ab³+16(b^4)
（a-b）的五次方和（a+2b）的四次方的展开式
(a-b)^5
=(a^5)-5(a^4)b+10a³b²-10a²b³+5a(b^4)-(b^5)
(a+2b)^4
=(a^4)+4a³(2b)+6a²(2b)²+4a(2b)³+(2b)^4
=(a^4)+8a³b+24a²b²+32ab³+16(b^4)