1.b+1/c=1,b=1-1/c=(c-1)/c
1/b=c/(c-1)
a+1/b=a+c/(c-1)=1
a(c-1)+c=c-1
ac-a=-1
ac+1=a
c+1/a=1
2.A^2+3A=1
两边同除以A得：A+3=1/A
A-1/A=-3
(A+1/A)^2=(A-1/A)^2+4=13
A+1/A=±√13
3.X^2-2x+M≠0,对任意的 x都成立.
即(x-1)^2+M-1≠0
M≠1-(x-1)^2
M>1