Question

[Trần Thiện Khiêm]

Gấp!!

Rút gọn: 

a) (a+b+c)^2-(a+b)^2-(a+c)^2-(b+c)^2

b) (a+b+c)^2+(a-b+c)^2+(a+b-c)^2+(-a+b+c)^2

Answer 1

[Moon Light]

a)(a+b+c)²-(a+b)²-(a+c)²-(b+c)²

=a²+b²+c²+2ab+2bc+2ca-a²-2ab-b²-a²-2ac-c²-b²-2bc-c²

=-a²-b²-c²

=-(a²+b²+c²)

b)(a+b+c)²-(a-b+c)²+(a+b-c)²+(-a+b+c)²

=a²+2ab+b²+2bc+c²+2ac-a²-b²-c²+2ab+2bc-2ac+a²+b²+c²+2ab-2bc-2ac+a²+b²+c²-2ab-2ac+2bc

=2a²+2b²+2c²+4ab-4bc-4ac