Bài 1:
`a)`
`(x^2+2)(2-3x)`
`=x^2(2-3x)+2(2-3x)`
`=2x^2-3x^3+4-6x`
`=-3x^3+2x^2-6x+4`
$\\$
`b)`
`(2x-3)(3x+2)-6x^2`
`=6x^2-5x-6-6x^2`
`=-5x-6`
$\\$
`c)`
`(3x-5y)(4x+7y)`
`=3x(4x+7y)-5y(4x+7y)`
`=12x^2+21xy-20xy-35y^2`
`=12x^2+xy-35y^2`
$\\$
`d)`
`(2x+3y)(3x-2y)-5(x^2-y^2)`
`=6x^2+5xy-6y^2-5x^2+5y^2`
`=(6x^2-5x^2)+(-6y^2+5y^2)+5xy`
`=x^2+5xy-y^2`
$\\$
Bài 2:
`a)`
`2x(x-5)-x(2x+3)=26`
`\to 2x^2-10x-2x^2-3x=26`
`\to -13x=26`
`\to x=-2`
Vậy `x=-2`
$\\$
`b)`
`(x+7)^2-x(x-3)=12`
`\to x^2+14x+49-x^2+3x=12`
`\to 17x=12-49`
`\to 17x=-37`
`\to x=-37/17`
Vậy `x=-37/17`
$\\$
`c)`
`(x+1)(x+2)-(x+2)(x+3)=0`
`\to (x+2)(x+1-x-3)=0`
`\to -2(x+2)=0`
`\to x+2=0`
`\to x=-2`
Vậy `x=-2`
