To find the value of x in the triangle problem, it is essential to apply the theorem that states the measure of an external angle equals the sum of the two opposite angles. Given that one of the opposite angles is 50 degrees, the angle adjacent to the external angle of 125 degrees can be calculated as 180 - 125. The next step involves using the supplementary angle property, where the sum of two angles on a straight line equals 180 degrees. Ultimately, the calculations lead to determining the value of x through geometric reasoning rather than specific formulas. Understanding these principles is crucial for solving the problem effectively.