For any real number \( x \), let \( [x] \) denote the largest integer less than equal to \( x \). Let \( f \) be a real valued function defined on the interval \( [-10,10] \) by 
. Then the value of \( \dfrac{\pi^{2}}{10}\displaystyle\int\limits_{-10}^{10} f(x)\cos \pi x \, dx \) is :
