Toán 8: Những hằng đẳng thức đáng nhớ

$\left(A+B\right)^2=A^2+AB+B^2$

$\left(A-B\right)^2=A^2-2AB+B^2$

$x^2+2xy+y^2=x^2+y^2$

$x^2-2xy+y^2=x^2-y^2$

$C^2+2CD+D^2=\left(C-D\right)^2$

$\left(x+y\right)^2=\left(x+y\right)\left(x+y\right)$

$x^2-y^2=\left(x+y\right)\left(x-y\right)$

$\left(-x-y\right)^2=\left(-x\right)^2-2\left(-x\right)y+y^2$

$\left(x+y\right)\left(x+y\right)=y^2-x^2$

$x^2+y^2=\left(x+y\right)^2+2xy$

$x^2+y^2=\left(x+y\right)^2-2xy$

$x^2-y^2=\left(x+y\right)^2-2xy$

$x^2+y^2=\left(x-y\right)^2-2xy$

$x^2+y^2=\left(x+y\right)^2$

$\left(x+y\right)^2=-\left(y+x\right)^2$

$\left(x-y\right)^2=\left(y-x\right)^2$

$\left(x-y\right)^3=\left(y-x\right)^3$

$\left(a+b+c\right)^2=a^2+b^2+c^2+2ab+2bc+2ac$

$\left(a+b+c\right)^2=a^2+b^2+c^2+2\left(ab+bc+ac\right)$

$\left(a-b+c\right)^2=a^2-b^2-c^2+2ab+2bc+2ac$

$\left(a+b-c\right)^2=a^2+b^2+c^2+2ab-2bc-2ac$

$\left(a-b-c\right)^2=a^2+b^2+c^2-2ab+2bc-2ac$

$4x^2-9y^2=\left(2x-3y\right)\left(2x+3y\right)$

$x-2=\left(\sqrt{x}+2\right)\left(\sqrt{x}-2\right)$

$x^2-1=\left(x+1\right)\left(x-1\right)$

$x^2-3=\left(x+\sqrt{3}\right)\cdot\left(x-\sqrt{3}\right)$

$x-1=\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)$

$x^2-4=\left(x-2\right)\left(x+2\right)$

$x^2-2x+1=\left(x-1\right)^2$

$\left(a+b+c\right)\left(a+b-c\right)=\left(a+b\right)^2-c^2$

$2-a=\left(\sqrt{2}+a\right)\left(\sqrt{2}-a\right)$

$x-2=\left(\sqrt{x}-\sqrt{2}\right)\left(\sqrt{x}+\sqrt{2}\right)$

$\left(c+d\right)^2-\left(a+b\right)^2=\left(c+d+a+b\right)\left(c+d-a+b\right)$

$\left(c-d\right)^2-\left(a+b\right)^2=\left(c-d+a+b\right)\left(c-d-a+b\right)$

$\left(a+b+c-d\right)\left(a+b-c+d\right)=\left(a+b\right)^2-\left(c-d\right)^2$

$\left(c-d\right)^2-\left(a-b\right)^2=\left(c-d+a-b\right)\left(c-d-a-b\right)$

$\left(c-d\right)^2-\left(a-b\right)^2=\left(c-d+a-b\right)\left(c-d-a+b\right)$