Question

In the figure above, the measure of <BDE is 20 and CD is perpendicular to DE. What is the measure of <ADC ?​

Answer 1

∠ ADC = 110°

Explanation:

∠ CDE = 90° ( angle between perpendicular lines ) , then

∠ CDB + ∠ BDE = 90°

∠ CDB + 20° = 90° ( subtract 20° from both sides )

∠ CDB = 70°

∠ ADC and ∠ CDB are adjacent angles on a straight line and sum to 180° , so

∠ ADC + ∠ CDB = 180° , that is

∠ ADC + 70° = 180° ( subtract 70° from both sides )

∠ ADC = 110°