Đáp án + Giải thích các bước giải:
`12.`
`a)` `(2x-3)^2=(2x)^2-2*2x*3+3^2=4x^2-12x+9`
`b)` `(5/2-x)^2=(5/2)^2-2*5/2*x+x^2=25/4-5x+x^2`
`c)` `(2x+3y)^2=(2x)^2+2*2x*3y+(3y)^2=4x^2+12xy+9y^2`
`d)` `(3x+2/3yz)^2=(3x)^2+2*3x*2/3yz+(2/3yz)^2=9x^2+4xyz+4/9y^2z^2`
`e)` `((xy)/2-x/3)((xy)/2+x/3)=((xy)/2)^2-(x/3)^2=(x^2y^2)/4-x^2/9`
`13.`
`a)` `16x^2+24x+9=(4x)^2+2*4x*3+3^2=(4x+3)^2`
`b)` `x^2/4-3x+9=(x/2)^2-2*x/2*3+3^2=(x/2-3)^2`.
