Lines \[\overleftrightarrow{AB}\] and \[\overleftrightarrow{CD}\] intersect at point \[O\]. Lines A B and C D intersect at point O. Angle A O D is labeled x. Angle B O D is labeled z. Angle B O C is labeled y. \[A\] \[B\] \[C\] \[D\] \[O\] \[x\] \[y\] \[z\] Complete the proof that vertical angles are congruent. Statement Reason 1 \[\overleftrightarrow{AB}\] and \[\overleftrightarrow{CD}\] intersect at point \[O\]. Given. 2 \[m \angle x + m \angle z = 180 \degree\] These angles are , so their measures sum to \[180 \degree\]. 3 \[m \angle y + m \angle z = 180 \degree\] Same as the previous reason. 4 \[m \angle x + m \angle z=\] Substitution (2, 3). 5 \[m \angle x = m \angle y\] Subtract \[m \angle z\] from both sides of the equation (4)