A triangle’s angles added up are 180 degrees and a triangle must have 3 angles, therefore the formula is: a + b + c = 180 So lets substitute the angles in your problem to the formula. Let a = 25 degrees Let b = 20 degrees And let c = x + 144
25 + 20 + (x + 144) = 180 Add common variables, in this case 25 and 20: 45 + (x + 144) = 180 Isolate the x variable, first by subtracting 45 from both sides. 45 - 45 + (x + 144) = 180 - 45 x + 144 = 135 Now, subtract both sides by 144: x + 144 - 144 = 135 - 144 x = -9 Your answer is: x = -9
