Which series represents f(x)=11+xf(x) = \frac{1}{1+x}f(x)=1+x1 for ∣x∣<1|x| < 1∣x∣<1?
∑n=0∞xn\sum_{n=0}^{\infty} x^n∑n=0∞xn
∑n=0∞(−1)nxn\sum_{n=0}^{\infty} (-1)^n x^n∑n=0∞(−1)nxn
∑n=0∞(−1)nx2n\sum_{n=0}^{\infty} (-1)^n x^{2n}∑n=0∞(−1)nx2n
∑n=0∞x2n\sum_{n=0}^{\infty} x^{2n}∑n=0∞x2n