Move words to the blanks and equations to the boxes to prove that vertical angles 21 and 23 are congruent. Because linear pairs of angles are
and
Because angles that are
to the same angle are
it can be concluded that 21 23.
congruent
m21 +m22 = 180°
supplementary
m22 + m23 = 180°
m2l + m23 = 180°