3/4x²-1.5=0
3x²=6
x²=2
x=±√2
（2x+3）²-（2x+3）-56=0
(2x+3-8)(2x+3+7)=0
(2x-5)(2x+10)=0
2x-5=0 2x+10=0
∴X1=2.5
X2=-5
x²-2（a-b）x-4ab=0
(x-2a)(x+2b)=0
x-2a=0 x+2b=0
∴X1=2a
X2=-2b
x²+3mx=54m²
x²+3mx-54m²=0
(x+9m)(x-6m)=0
x+9m=0 x-6m=0
∴X1=-9m
X2=6m