Since the triangle DEF is an equilateral triangle and x is the height of this triangle, we can use the following formula for the height of an equilateral triangle:
[tex]h=\frac{l\sqrt[]{3}}{2}[/tex]Where 'l' is the length of the triangle side.
So, using l = 13, we have:
[tex]\begin{gathered} x=\frac{13\cdot\sqrt[]{3}}{2} \\ x=\frac{13\cdot1.73}{2} \\ x=11.2 \end{gathered}[/tex]So the value of x is 11.2
