解:2(X+3)²=X(X+3) 2(x²+6x+9)=x²+3xx²+9x+18=0(x+3)(x+6)=0所以x1=-3,x2=-6
(X+3)²=X(X+3)(X+3)²-X(X+3)=0(x+3)(x+3-x)=03(x+3)=0x+3=0x= -3