Solution
= Solution
For $t>2$, the <Heaviside step function> contributes a constant unit forcing. Solving the resulting <first-order linear differential equation> from the value at $t=2$ gives
$$
\boxed{T_1(t)=T_\infty+(\Delta-e^a)e^{-at}
+\frac1a\left(1-e^{-a(t-2)}\right)}.
$$