北师大版,一元二次方程、、、

1.
(2x-3)(x+1)=0
x1=3/2,x2=-1
2.
4^2-(m-3)*4-3m=0
m=4
4x2=-3m=-12
x2=-3
3.
设路面宽x
(48-2x)(24-2x)=(5/9)48*24
(x-24)(x-12)=160
x^2-36x+128=0
(x-32)(x-4)=0
x=4 (x=36舍弃）
4.
6x²-x-12=0
x^2-(1/6)x-2=0
(x^2-(1/6)x+(1/12)^2)-(289/144)=0
(x-(1/12))^2=(17/12)^2
x-(1/12)=+ -(17/12)
x=(1/12)+ -(17/12)
x1=3/2,x2=-4/3