1. **Problem statement:** You meant a triangle, not a rectangle, and you want an image plus help finding its angles. 2. **Key formula / rules:** The sum of the interior angles of any triangle is $180^\circ$. $$A+B+C=180^\circ$$ If you know two angles, you can find the third by subtracting their sum from $180^\circ$. 3. **How to find a missing angle:** - Add the angles you already know. - Subtract that total from $180^\circ$. $$\text{missing angle}=180^\circ-\text{known angle 1}-\text{known angle 2}$$ 4. **Important rules:** - The three angles of a triangle always add to $180^\circ$. - In a right triangle, one angle is $90^\circ$. - In an equilateral triangle, all angles are $60^\circ$. 5. **Example:** If a triangle has angles $50^\circ$ and $60^\circ$, then the third angle is: $$180^\circ-50^\circ-60^\circ=70^\circ$$ 6. **Final answer:** A triangle’s angles always add to $180^\circ$, so you find a missing angle by subtracting the other two from $180^\circ$.