Consider the diagram and proof by contradiction.
Given: AABC with 2B - C
Prove: AB - AC
It is given that B C. Assume AB and AC are not
congruent. If AB > AC, then mC >m_B by _
AC > AB, then m B >m_C for the same reason. However,
using the given statement and the definition of
congruency, we know that m B = m_C. Therefore, AB =
AC and AB AC.
What is the missing reason in the proof?
O converse of the triangle parts relationship theorem
substitution
O definition of congruency
O converse of the isosceles triangle theorem