Đáp án:
`1)x=3/2`
`2)x=-6/11`
`3)x=5/2`
Giải thích các bước giải:
`1)4x(x-5)-7x(x-4)+3x²=12`
`⇔4x²-20x-7x²+28x+3x²=12`
`⇔(4x²-7x²+3x²)+(-20x+28x)=12`
`⇔8x=12`
`⇔x=12/8`
`⇔x=3/2`
Vậy `x=3/2`
`2)4x²-2x+3-4x(x-5)=7x-3`
`⇔4x²-2x+3-4x²+20x=7x-3`
`⇔(4x²-4x²)+(-2x+20x)+3=7x-3`
`⇔18x+3=7x-3`
`⇔18x-7x=-3-3`
`⇔11x=-6`
`⇔x=-6/11`
Vậy `x=-6/11`
`3)3(5x-1)-x(x-2)+x²-13x=7`
`⇔15x-3-x²+2x+x²-13x=7`
`⇔(-x²+x²)+(15x+2x-13x)-3=7`
`⇔4x-3=7`
`⇔4x=7+3`
`⇔4x=10`
`⇔x=10/4`
`⇔x=5/2`
Vậy `x=5/2`
