是不是3倍根号2?
(x-3倍根号2)²=4(x-3倍根号2)
(x-3倍根号2)²-4(x-3倍根号2)=0
(x-3倍根号2)(x-3倍根号2-4)=0
(x-3倍根号2)[x-(3倍根号2+4)]=0
x1=3倍根号2,x2=3倍根号2+4