[1KD]Prerequisites:[0G0]↺↻.Given \( f(t)=∑_{k=0}^∞ a_ k t^ k\) with \(a_ k≥ 0\), such that the radius of convergence is \(r{\gt}0\), show that \(\lim _{t→ r-}f(t)=f(r)\).
[1KF]↺↻
