Solution (source code)

= Solution

The <characteristic equation of a linear recurrence> is
$$
r^2-2r+1=(r-1)^2=0.
$$
Its repeated root gives
$$
\boxed{y_n=A+Bn}.
$$
Since $t_n=nh$, this can be written $y_n=A+(B/h)t_n$, exactly the discrete form of the continuous solution $y(t)=C+Dt$ of $y''=0$.