2.1.66 Calculation of limits
condition: Find \( d y / d x \) and \( d^{2} y / d x^{2} \) for the given functions: a) \( y=\frac{x}{\left(x^{2}-1\right)} \), b) \( x=\cos \left(\frac{t}{2}\right), y=t-\sin t \)
Calculation of various limits, using L'Hopital's rule, remarkable limits, power series, equivalent values of various other methods.