1. **Problem:** Find the unknown angle in a triangle with angles 65°, 57°, and ?. 2. **Formula:** The sum of angles in any triangle is always 180°. That is, $$\text{Angle}_1 + \text{Angle}_2 + \text{Angle}_3 = 180^\circ$$ 3. **Apply the formula:** $$65^\circ + 57^\circ + x = 180^\circ$$ 4. **Calculate the unknown angle:** $$x = 180^\circ - (65^\circ + 57^\circ)$$ $$x = 180^\circ - 122^\circ$$ $$x = 58^\circ$$ 5. **Answer:** The unknown angle is **58°**. This method works because the sum of interior angles in any triangle is always 180 degrees, so subtracting the sum of known angles from 180 gives the missing angle.