Chú ý:
$(A-B)^2=(-B-A)^2=(B-A)^2$
$(A+B)^2=A^2+2AB+B^2$
Bài làm:
$(a-b+c)^2-(c-b)^2+2(a-b+c)(b-c)$
$= (a-b+c)^2+(b-c)^2+2(a-b+c)(b-c)$
$= (a-b+c)^2+2(a-b+c)(b-c)+(b-c)^2$
$= [(a-b+c)+(b-c)]^2$
$= a^2$
`(a-b+c)^2 - (c-b)^2 + 2(a-b+c)(b-c)`
`= (a-b+c)^2 + (b-c)^2 + 2(a-b+c)(b-c)`
`= (a-b+c)^2 + 2(a-b+c)(b-c) + (b-c)^2`
`= [(a-b+c) + (b-c)]^2`
`= (a - b + c + b -c)^2`
`= a^2`
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