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:
![h=\frac{l\sqrt[]{3}}{2}](https://img.qammunity.org/2023/formulas/mathematics/college/p6du5rbgd12mj61ejyxqwp9ganm1wg9ohk.png)
Where 'l' is the length of the triangle side.
So, using l = 13, we have:
![\begin{gathered} x=\frac{13\cdot\sqrt[]{3}}{2} \\ x=(13\cdot1.73)/(2) \\ x=11.2 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/lhceiwljy1oigww4zaipbqbjo27u5dswlm.png)
So the value of x is 11.2