To make things easier to understand, let's see this figure, which represents the given situation:
According to this diagram, to find x, which is the length of the side of the triangle, we can use pythagorean theorem, this way:
[tex]\begin{gathered} x^2=(\frac{x}{2})^2+5^2 \\ x^2=\frac{x^2}{4}+25 \\ x^2-\frac{x^2}{4}=25 \\ \frac{3}{4}x^2=25 \\ x^2=\frac{25}{3}\cdot4^{} \\ x=\sqrt[]{33.3333} \\ x=5.77 \end{gathered}[/tex]
