Answer:
Step-by-step explanation:
Consider triangle ACD. This triangle is isosceles triangle, because AD = DC. Angles adjacent to the base AC are congruent abgles, so
The sum of the measures of all interiror angles in the triangle is always then
Angles ADC and BDC are supplementary angles (add up to ), then
Consider triangle BCD. This triangle is isosceles triangle because BC = DC. Angles adjacent to the base BD are congruent abgles, so
The sum of the measures of all interiror angles in the triangle is always then