第一题;（a+b)²(a²-2ab+b²)=

（a+b)²(a²-2ab+b²)
=(a+b)²(a-b)²
=[(a+b)(a-b)]²
=(a²- b²)²
=a的4次方-2a²b²+b的4次方
(x+5)²-(x-2)(x-3)
=x²+10x+25-x²+5x-6
=15x+19
(a+2b-c)(a-2b-c)
=[(a-c)+2b][(a-c)-2b]
=(a-c)²-4b²
=a²-2ac+c²-4b²
(a+b+c)²
=[(a+b)+c]²
=(a+b)²+2c(a+b)+c²
=a²+2ab+b²+2ac+2bc+c²