\(\left(x+1\right)\left(x-1\right)=x^2-x+x-1=x^2-1\)
\(\left(x-2y\right)\left(x+2y\right)=x^2+2xy-2xy-4y^2=x^2-4y^2\)
\(\left(x+1\right).\left(x-1\right)\)
\(=x^2-x+x-1\)
\(=x^2+\left(-x+x\right)-1\)
\(=x^2-1.\)
\(\left(x-2y\right).\left(x+2y\right)\)
\(=x^2+2xy-2xy-4y^2\)
\(=x^2+\left(2xy-2xy\right)-4y^2\)
\(=x^2-4y^2.\)
Chúc bạn học tốt!
1) \((x+1) . (x-1)\) \(= x^2 - x + x - 1\)
\(= x^2 - 1\)
2) \((x-2y).(x+2y)\) \(= x^2 + 2xy - 2xy - 4y^2\)
\(=x^2-4y^2\)
học tốt nhé !
