Fill in the missing blanks below to prove that the Sum of the measures of the interior angles of a triangle is 180°.
Let triangle ABC be any triangle. Draw line DE, which passes through point A, parallel to ___________ with a compass and straightedge. According to the Angle Addition Postulate ∡DAC + ∡CAB + ∡BAE = ∡DAE. ∡DAC is congruent to ∡BCA by Alternate Interior Angles. ∡BAE is congruent to ____________ by the same theorem. Substitution allows me to replace ∡DAC with ∡BCA and ∡BAE with ∡ABC in the equation. Therefore, __________________________= ∡DAE. By definition of a straight angle, ∡DAE meas

Question

Fill in the missing blanks below to prove that the Sum of the measures of the interior angles of a triangle is 180°. 
Let triangle ABC be any triangle. Draw line DE, which passes through point A, parallel to ___________ with a compass and straightedge. According to the Angle Addition Postulate ∡DAC + ∡CAB + ∡BAE = ∡DAE. ∡DAC is congruent to ∡BCA by Alternate Interior Angles. ∡BAE is congruent to ____________ by the same theorem. Substitution allows me to replace ∡DAC with ∡BCA and ∡BAE with ∡ABC in the equation. Therefore, __________________________= ∡DAE. By definition of a straight angle, ∡DAE meas

anonymous · Answer

[continued] measures 180°. Consequently, the three angles of ABC (BCA, CAB, and ABC) measure 180° by substitution.

anonymous · Answer

@dan815 @ParthKohli @imqwerty help please?

imqwerty · Answer

CB
∡ABC
∡BCA+∡CAB+∡ABC