Find the sum of ∑n=0∞(n+1)xn\sum_{n=0}^{\infty} (n+1) x^n∑n=0∞(n+1)xn for ∣x∣<1|x|<1∣x∣<1.
(1−x)−1(1-x)^{-1}(1−x)−1
(1−x)−2(1-x)^{-2}(1−x)−2
(1+x)−2(1+x)^{-2}(1+x)−2
(1−x)−3(1-x)^{-3}(1−x)−3