Đáp án+Giải thích các bước giải:
`(a+b-c)^2`
$*$ Cách 1:
`(a+b-c)^2`
`=[(a+b)-c]^2`
`=(a+b)^2-2.(a+b).c+c^2`
`=a^2+2ab+b^2-2c(a+b)+c^2`
`=a^2+2ab+b^2-2ac-2bc+c^2`
`=a^2+b^2+c^2+2ab-2ac-2bc`
$*$ Cách 2:
`(a+b-c)^2`
`=[a+(b-c)]^2`
`=a^2+2a.(b-c)+(b-c)^2`
`=a^2+2ab-2ac+b^2-2bc+c^2`
`=a^2+b^2+c^2+2ab-2ac-2bc`
`(a-b-c)^2`
$*$ Cách 1:
`(a-b-c)^2`
`=[(a-b)-c]^2`
`=(a-b)^2-2.(a-b).c+c^2`
`=a^2-2ab+b^2-2c(a-b)+c^2`
`=a^2-2ab+b^2-2ac+2bc+c^2`
`=a^2+b^2+c^2-2ab-2ac+2bc`
$*$ Cách 2:
`(a-b-c)^2`
`=[a-(b+c)]^2`
`=a^2-2a.(b+c)+(b+c)^2`
`=a^2-2ab-2ac+b^2+2bc+c^2`
`=a^2+b^2+c^2-2ab-2ac+2bc`
