Are these two series of the arctangent function the same?

52 Views Asked by At

I came across the series axpansion of the arctangent function shown here: $$ \tag{1}\arctan(x)=\sum_{k=0}^\infty\frac{4^kx^{2k+1}}{(2k+1)\binom{2k}{k}\left(1+x^2\right)^{k+1}}. $$ Is it possible to rearrangenge the equation above as the series expansion $$ \tag{2}\arctan(x)=\frac{i}2\sum_{k=1}^\infty\frac{x^n}{n}\left(\frac{1}{(x+i)^n}-\frac{1}{(x-i)^n}\right) $$ that was derived in this paper? In other words, can we derive equation (2) directly from equation (1)?