Bài 3 vận dụng:
\(\left(x+y\right)^2-\left(x-y\right)^2=\left(x^2+2xy+y^2\right)-\left(x^2-2xy+y^2\right)\\ =\left(x^2-x^2\right)-\left(-2xy-2xy\right)+\left(y^2-y^2\right)=4xy=VP\left(đpcm\right)\)
\(Bài.2\left(TH\right):\\ A=\left(3x+2\right)^2+\left(2x-7\right)^2-2\left(3x+2\right)\left(2x-7\right)=\left[\left(3x+2\right)-\left(2x-7\right)\right]^2\\ =\left(x+9\right)^2\\ Thay:x=-19.vào.A.rút.gọn:A=\left(x+9\right)^2=\left(-19+9\right)^2=\left(-10\right)^2=100\\ Vậy:A=100.khi.x=-19\)
3:
(x+y)^2-(x-y)^2
=(x+y+x-y)(x+y-x+y)
=2x*2y=4xy
2:
\(A=\left(3x+2\right)^2-2\left(3x+2\right)\left(2x-7\right)+\left(2x-7\right)^2\)
\(=\left(3x+2-2x+7\right)^2=\left(x+9\right)^2\)
Khi x=-19 thì A=(-19+9)^2=(-10)^2=100
1:
a: =x^2+2xy+y^2+x^2-2xy+y^2
=2x^2+2y^2
b: =(x+y)^2+2(x+y)(x-y)+(x-y)^2
=(x+y+x-y)^2=(2x)^2=4x^2
