∴.
∴.
(2) The symmetry axis of ∵ cn is perpendicular to the X axis, and the vertex is Pn.
∴ Let the equation of Cn hold.
Substitute Dn(0, n2+ 1) into the above formula to get a= 1.
The equation of ∴Cn is y = x2+(2n+3) x+N2+ 1.
∫kn = y ' | x = 0 = 2n+3,
∴,
∴==.
(3)t={y|y=﹣( 12n+5),n∈n*}={y|y=﹣2(6n+ 1)﹣3,n∈n*},
∴S∩T=T, and the maximum number in t is a 1 = ∩ 17.
Let {an} tolerance be d, then ﹣ a10 = ﹣17+9d ﹣ (﹣ 265125. )
This led to.
∫ An ∈∴d = 12m(m∈n *)
∴d=﹣24,
∴an=7﹣24n(n∈N*,n≥2).