TeX source:
\begin{array}{rcl}f\left(-\dfrac{5}{11}\right) &=& \sqrt{104\cdot\left(-\dfrac{5}{11}\right)^2+36}-\sqrt{225\cdot\left(-\dfrac{5}{11}\right)^2+11}\\&=& \sqrt{\dfrac{6.956}{121}}-\sqrt{\dfrac{6.956}{121}}\\&=& 0\end{array}