`1/`
`a)A=(2x+3)^2+(4x^2-6x+9)-2(4x^3-1)`
`=4x^2+12x+9+4x^2-6x+9-8x^3+2`
`=-8x^3+8x^2+6x+11`
`b)B=(x+1)^3-4x(x+1)(x-1)+3(x-1)(x^2+x+1)`
`=x³+3x²+3x+1-4x(x²-1)+3(x³-1)`
`=x^3+3x^2+3x+1-4x^3+4x+3x^3-3`
`=3x^1+7x-2`
Bài `2:`
`a)x^2-y^2-3x+3y`
`=(x-y)(x+y)-3(x-y)`
`=(x-y)(x+y-3)`
`b)(y-x)²+(x-y)(3x-2y)-x^2+y^2`
`=y²-2xy+x²+3x²-2xy-3xy+2y²-x²+y²`
`=4y²-7xy+3x^2`
`=4y²-4xy-3xy+3x²`
`=4y(y-x)-3x(y-x)`
`=(y-x)(4y-3x)`
Bài `3:`
`(2x-1)^2-(3x+4)^2=0`
`⇔4x²-4x+1-9x²-24x-16=0`
`⇔-5x²-28x-15=0`
`⇔-(5x²+3x+25x+15)=0`
`⇔x(5x+3)+5(5x+3)=0`
`⇔(5x+3)(x+5)=0`
`⇔x=-3/5` hoặc `x=-5`