Answer:
for the first triangle, the length of the third side is 37 units
for the second triangle, the length of the third side is 29 units
Step-by-step explanation:
Given the triangles in the attached image.
Let us apply the Pythagorean theorem to solve for the third side.

For the first triangle;

substituting the values;
![\begin{gathered} c=\sqrt[]{12^2+35^2} \\ c=\sqrt[]{1369} \\ c=37 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/t2iyv78e7tg9thh6uhq9stywun5am5fuep.png)
For the second triangle;

substituting the values;
![\begin{gathered} c=\sqrt[]{20^2+21^2} \\ c=\sqrt[]{841} \\ c=29 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/wyay5mb1fxtiakakkz3kgp0iiilm96bu66.png)
Therefore, for the first triangle, the length of the third side is 37 units
for the second triangle, the length of the third side is 29 units