(a-1)x^2-(a^2+2)x+(a^2+2a)=0
(x-a)[(a-1)x-(a+2)]=0
x=a或x=(a+2)/(a-1)
(b-1)x^2-(b^2+2)x+(b^2+2b)=0
(x-b)[(b-1)x-(b+2)]=0
x=b或x=(b+2)/(b-1)
a-1不等于b-1,a,b不相等,公共根只能是x=a=(b+2)/(b-1)或x=b=(a+2)/(a-1)
a=(b+2)/(b-1)=(b-1+3)/(b-1)=1+3/(b-1)
a,b為正整數(shù),b只能為2,4
b=2時(shí),a=4
b=4時(shí),a=2
a,b為2和4. a=2時(shí),b=4 a=4時(shí),b=2