WILL GIVE BRAINLIEST! LOTS OF POINTS! MULTIPLE CHOICE Triangle ABC is a right triangle. Point D is the midpoint of side AB, and
point E is the midpoint of side AC. The measure of ∠ADE is 47°. The proof, with a missing reason, proves that the measure of ∠ECB is 43°. Statement Reason m∠ADE = 47° Given m∠DAE = 90° Definition of a right angle m∠AED = 43° ? segment DE joins the midpoints of segment AB and segment AC Given segment DE is parallel to segment BC Midsegment of a Triangle Theorem ∠ECB ≅ ∠AED Corresponding angles are congruent m∠ECB = 43° Substitution property Which theorem can be used to fill in the missing reason? A. Concurrency of Medians Theorem B. Isosceles Triangle Theorem C. Triangle Inequality Theorem D. Triangle Sum Theorem
I believe it is that since we are given two angles, D is 47 and A is 90. Using the Triangle Sum Theorem, we know that a triangle's angles equals to 180 degrees so, 90+47=137, then 180-137=43.