Question

运用乘法公式计算 （a-b+c)的平方 （a+b+c）（a-b-c) 并且写出公式

Answer 1

(a-b+c)²
=[(a+b)+c]²
=(a+b)²+2c(a+b)+c²
=a²+2ab+b²+2ac+2bc+c²
=a²+b²+c²+2ab+2ac+2bc
(a+b+c)(a-b-c)
=[a+(b+c)][a-(b+c)]
=a²-(b+c)²
=a²-(b²+2bc+c²)
=a²-b²-c²-2bc