a(a-1)+(b-a的平方)=-7求(二分之a的平方b的平方)-ab

a(a-1)+(b-a²)
=a²-a+b-a²
=-a+b
=-7
a-b=7

(a²+b²)/2-ab
=(a²-2ab+b²)/2
=(a-b)²/2
=7²/2
=49/2

(a-2b+3c)(a-2b+3c)-(a+2b-3c)(a+2b-3c)
=(a-2b+3c)²-(a+2b-3c)²
=[(a-2b+3c)+(a+2b-3c)][(a-2b+3c)-(a+2b-3c)]
=2a*(-4b+6c)

如果是因式分解
则=4a(3c-2b)

如果是计算
则=-8ab-12ac