40.
We have to use the two-tangent theorem, to solve this.
The Two-Tangent Theorem states that if two tangent segments are drawn to one circle from the same external point, then they are congruent.
So, we can say:
[tex]\begin{gathered} 2x^2+5=13 \\ \end{gathered}[/tex]
We can now solve this for x:
[tex]\begin{gathered} 2x^2+5=13 \\ 2x^2=13-5 \\ 2x^2=8 \\ x^2=\frac{8}{2} \\ x^2=4 \\ x=\pm\sqrt[]{4} \\ x=2 \\ x=-2 \end{gathered}[/tex]
