\(a,\left(x+y\right)^2-2\left(x+y\right)\left(x-y\right)+\left(x-y\right)^2\\ =\left[\left(x+y\right)-\left(x-y\right)\right]^2\\ =\left(x+y-x+y\right)^2\\ =y^2\\ b,\left(x+y\right)^2-\left(x-y\right)^2=\left[\left(x+y\right)-\left(x-y\right)\right]\left[\left(x+y\right)+\left(x-y\right)\right]\\ =\left(x+y-x+y\right)\left(x+y+x-y\right)\\ =2y.2x=4xy\)
\(Bài2\\ \)
bạn xem lại đề câu a nhé
\(b,126^2-126.152+5776\\ =126^2-2.76.126+76^2\\ =\left(126-76\right)^2\\ =50^2=2500\)
bài 1
a)
\(=x^2+2xy+y^2-2\left(x^2-y^2\right)+x^2-2xy+y^2=x^2+2xy+y^2-2x^2+2y^2+x^2-2xy+y^2=4y^2\)
b)
\(=\left(x+y-x-y\right)\left(x+y+x-y\right)=x^2\)
bài 2
a)
153^2 + 94 * 153 + 47^2
= 153 * (153 + 94) + 47^2
= 153 * 247 + 47^2
= 153 * (200 + 47) + 47^2
= 153 * 200 + 153 * 47 + 47^2
= 153 * 200 + 47 * (153 + 47)
= 153 * 200 + 47 * 200
= 200 * (153 + 47)
= 200 * 200
= 40000
b)126^2 - 152.126 + 5776
= 126 . 126 - 152.126 +126. 2888/63
= 126 . ( 126 - 152 + 2888/63)
= 126 . 1250/63
= 2500
