The are of a triangle is:

b is the base and h is the height
In the given triangle the base is Leg BC and the height is Leg AB:

Use the equation above to solve AB:
![\begin{gathered} \text{Multiply both sides of the equation by 2:} \\ 12.5*2=2*(1)/(2)AB^2 \\ \\ 25=AB^2 \\ \\ \text{Take the square root of both sides of the equation:} \\ \sqrt[]{25}=√(AB^2) \\ \\ 5=AB \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/xalg3na2nnjch5gt5gorudb1yuwf0lj4ke.png)
Then, Legs of the given right triangle have a measure of 5.
To find the measure of the hypotenuse use Pythagorean theorem:
![\begin{gathered} \text{hypotenuse}^2=Leg1^2+Leg2^2 \\ \text{hypotenuse}=\sqrt[]{Leg1^2+Leg2^2} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/dxxgxuxdwg1kry67tgnmu4ghgz4mu0x902.png)
![\begin{gathered} \text{hypotenuse}=\sqrt[]{5^2+5^2} \\ \\ \text{hypotenuse}=\sqrt[]{25+25} \\ \\ \text{hypotenuse}=\sqrt[]{50} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/pjl0ba0g97iw85ew3iyyv86dh5v2h8vu38.png)
Find the prime factorization of 50 to simplify it:

![\begin{gathered} \text{hypotenuse}=\sqrt[]{2*5^2} \\ \\ \text{hypotenuse}=5\sqrt[]{2} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/txjhc6s1192k0hrqta6u3itlxab2o0ybnz.png)