19.(1) 解:(x-3)+2x(x-3)=0
(x-3)(x-3+2x)=0
(x-3)(3x-3)=0
可得x-3=0或3x-3=0
所以x=3或x=1
(2)(2x+3)^2-4(2x-5)^2=0
[(2x+3)+2(2x-5)][(2x+3)-2(2x-5)]=0
(6x-7)(-2x+13)=0
∴6x-7=0或-2x+13=0
∴x=7/6或x=13/2
20.(1)(x+3)(x+1)=6x+5
+4x+3=6x+5
-2x=2
2x+1=2+1
( x-1)=3
x-1=±√3
x=1-√3,x=1+√3
(2)解:2﹙x-2﹚-5﹙x-1﹚+2=0
[2﹙x-1﹚+1][﹙x-1﹚+2]=0
﹙2x-1﹚﹙x+1﹚=0
x1=1/2
你是要问19还是20?