29.35. Calculate the length of the arc of the curve $y=\operatorname{ch} x$, enclosed between the points $\left(x_{1}, y_{1}\right)$ and $\left(x_{2}, y_{2}\right)$.
29.35. It is clear that $y^{\prime}=\operatorname{sh} x$ and $\sqrt{1+\left(y^{\prime}\right)^{2}}=\operatorname{ch} x$. Therefore, the length of the considered arc is $\int_{x_{1}}^{x_{2}} \operatorname{ch} x d x=\operatorname{sh} x_{2}-\operatorname{sh} x_{1}$ (it is assumed that $\left.x_{1}<x_{2}\right)$.

