x^2+y^2-2tx-2y+1=0.
x^2+y^2-2x-2ty+1=0.
x^2+y^2-2tx-2y+1=x^2+y^2-2x-2ty+1.
(t-1)(x-y)=0.
x=y.
2x^2-2(t+1)x+1=0.
(t+1)^2>2.