question:A telephone cable susbended between two poles 20 meters appart hangs in a curve with equation: $\displaystyle y=10(e^{\frac{x}{20}}+e^{\frac{-x}{20}})$ where -10<=x<=10

how long is the cable?

work:using the formula $\displaystyle L=2\int_0^{10} \sqrt{1+(\frac{dy}{dx})^2}dx$

this gives me an impossible (beyond my level) integral to solve