J. Yook' solution is correct. Note $\int \frac{2t}{t^2-1} \,dt = \ln (1-t^2)+ \ln C$ as numerator is a derivative of denominator (no need to invoke partial fractions). It should be also noted that we are talking about interval $(-1,1)$ as $t=\pm 1$ are breaking points (senior coefficient vanishes there) and $t=0$ selects this interval.