Đáp án + Giải thích các bước giải:
1)
`(x-1)^2=x^2-2.x.1+1^2=x^2-2x+1`
`(y-4)^2=y^2-2.y.4+4^2=y^2-8y+16`
`-(2y-5)^2=-[(2y)^2-2.2y.5+5^2]=-(4y^2-20y+25)=-4y^2+20y-25`
`(1-5a)^2=1^2-2.1.5a+(5a)^2=1-10a+25a^2`
`(1/3x-3y)^2=(1/3x)^2-2. 1/3x.3y+(3y)^2=1/9x^2-2xy+9y^2`
2)
`(x-1)(x+1)=x^2-1^2=x^2-1`
`(y-5)(y+5)=y^2-5^2=y^2-25`
`-(5+4y)(5-4y)=-(5-4y)(5+4y)=-[5^2-(4y)^2]=-(25-16y^2)=-25+16y^2`
`(2x-3)(2x+3)=(2x)^2-3^2=4x^2-9`
`(1/2x-2y)(1/2x+2y)=(1/2x)^2-(2y)^2=1/4x^2-4y^2`
