Explanation:
The sum of two interior angles in a triangle is equal to an exterior angle that is supplementary to the third interior angle.
Based on the above-mentioned information, we can write the following equation:
40 + 2x + 20 = 3x + 10
2x + 60 = 3x + 10
- Transfer like terms to the same side of the equation.
60 - 10 = 3x - 2x
40 = x
Replace x with 40 to find the measure of ∠BCD:
3 × 40 + 10 = 130