Mackenzie wrote the following paragraph proof for the vertical angles theorem: line segment nt intersects line segment mr forming four angles. angles 1 and 3 are vertical angles. angles 2 and 4 are vertical angles. the sum of angle 1 and angle 4 and the sum of angle 3 and angle 4 are each equal to 180 degrees by the definition of supplementary angles. the sum of angle 1 and angle 4 is equal to the sum of angle 3 and angle 4 angle 1 is equal to angle 3 by the subtraction property of equality. which phrase completes the proof? by construction using a straightedge by the definition of a perpendicular bisector by the transitive property of equality. by the vertical angles theorem