PutnamSuperchallengeIntegrals I: Feynman's Trick ShareIntegrals I: Feynman's Trick · Superchallenge problemEvaluate ∑k=1∞k(25)k\displaystyle\sum_{k=1}^{\infty} k\left(\frac{2}{5}\right)^{k}k=1∑∞k(52)k.Check Show answer Walk through it step by step Practice more like this Review this concept