How do you find the measurement of a side of a triangle if you have the measurement of 2 sides?

If it is a right triangle (one angle is exactly 90 degrees) it is much easier: use the Pythagorean Theorem. Pythagorean Theorem states that for right triangles: a2 + b2 = c2 Where a and b represent the length of the sides adjacent (next to) to the right angle, and c represents the length of the side opposite the triangle. Plug the two sides you do know into this equation to get the third. If it is an equilateral triangle, then all sides are the same by definition. If it is an isosceles triable, then remember that two sides are equal to each other. If it is none of these then I believe you need to provide more information in order to get help.