ANSWER
The length of the third leg is
Explanation:
The figure given is a right-angled triangle.
To find the third length of the triangle, we need to apply Pythagora's theorem
It states that

The third length of the triangle is the hypotenuse because it is the longest
![\begin{gathered} (Hypotenuse)^2=4^2+2^2 \\ (Hypotenuse)^2\text{ = 16 + 4} \\ (Hypotenuse)^2\text{ = 20} \\ \text{ Take the squareroots of both sides} \\ \text{ }\sqrt[]{(Hypotenuse)^2\text{ }}\text{ = }\sqrt[]{20} \\ \text{Hypotenuse = }4.472 \\ \text{Hypotenuse }\approx\text{ 4.5} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/8upn6q0r9tfe0hgcinzhijobc0memyj328.png)
Hence, the length of the third leg is 4.5