Đáp án:
Giải thích các bước giải:
$a)(x+y)^2+(x-y)^2_{}$
$⇔x^2+2xy+y^2+x^2-2xy+y^2_{}$
$⇔2x^2+2y^2_{}$
$b)2(x-y)(x+y)+(x+y)^2+(x-y)^2_{}$
$⇔2(x^2-y^2)+x^2+2xy+y^2+x^2-2xy+y^2_{}$
$⇔2x^2-2y^2+x^2+2xy+y^2+x^2-2xy+y^2_{}$
$⇔4x^2_{}$
$c)(x-y+z)^2+(z-y)^2+2(x-y+z)(y-z)_{}$
$⇔(x-y+z)^2+(z-y)^2+2(x-y+z).[ -(z-y)]_{}$
$⇔(x-y+z)^2+(z-y)^2-2(x-y+z)(z-y)_{}$
$⇔(x-y+z)^2-2(x-y+z)(z-y)+(z-y)^2_{}$
$⇔[ x-y+z-(z-y)]^2_{}$
$⇔(x-y+z-z+y)^2_{}$
$⇔x^2_{}$