1、2x（x²+9）=20x²
2x(x²+9-10x)=0
2x(x-9)(x-1)=0
解得x1=0 x2=9 x3=1
2、（1/3）x²-2x+3=3（2x+5）²
x²-6x+9-9(2x+5)²=0
(x-3)²-(6x+15)²=0
(x-3-6x-15)(x-3+6x+15)=0
(-5x-18)(7x+12)=0
(5x+18)(7x+12)=0
解得x1=-18/5 x2=-12/7
3、（2- √3）x²+（3-2√3）x-2=0
2- √3 -1
1 2
故[(2- √3)x-1](x+2)=0
解得x1=1/(2- √3)=2+√3
x2=-2