To determine whether the Pythagorean Theorem can be used on a triangle, you need to know whether the triangle is a right triangle. The Pythagorean Theorem states that in a right triangle, the square of the length of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the lengths of the other two sides:
\[ c^2 = a^2 + b^2 \]
If the triangle in question is a right triangle, then the answer is Yes. If it is not a right triangle (for example, an obtuse or acute triangle), then the answer is No.
So, if you know the type of triangle you are referring to, you can answer accordingly.