1,(x-1)(x+2)-x^2+3=5
⇔x^2+2x-x-2-x^2+3=5
⇔x+1=5
⇔x=4
vậy.......
2,(x-1)(x+3)=x^2+3
⇔x^2+3x-x-3=x^2+3
⇔x^2-2x-x^2=3+3
⇔-2x=6
⇔x=-3
vậy.......
3,(x-2)(3x+4)=3x(x-2)
⇔3x^2+4x-6x-8=3x^2-6x
⇔3x^2-3x^2+4x-6x+6x=8
⇔4x=8
⇔x=2
vậy.......
4,x-(x+2)(x-1)=3-x^2
⇔x-x^2+x-2x+2=3-x^2
⇔x-x^2+x-2x+x^2=3-2
⇔0=1(vô lý)
vậy phương trình vô nghiệm
5,(x+3)(x-1)-(x+4)(x+2)=8
⇔x^2-x+3x-3-x^2-2x-4x-8=8
⇔-8x=16
⇔x=-2
vậy........
6,(x-1)(x-2)-(x-3)(x-4)=0
⇔x^2-2x-x+2-x^2+4x+3x-12=0
⇔4x=12
⇔x=3
vậy.......
7,6(x-3)(x-1)-6(x^2+2)=36
⇔6x^2-6x-18x+18-6x^2+12=36
⇔-24x=36-18-12
⇔-24x=6
⇔x=-1/4
vậy.......
