Question

A student writes an incorrect step while checking if the sum of the measures of the two remote interior angles of triangle ABC below is equal to the measure of the exterior angle.

Step 1: m∠a + m∠b + m∠c = 180° (sum of angles of a triangle)
Step 2: m∠d − m∠c = 90° (complementary angles)
Step 3: Therefore, m∠a + m∠b + m∠c

Answer 1

d-c is not 90. It could only be 90 if it were a vertical line perpendicular to line BC