Geometry
posted by David .
Write a two column proof.
Given: angle STV is congruent to angle TVU, angle STU is congruent to angle UVS.
Prove: Angle SVT is congruent to angle UTV.

Draw a diagram.
SVU = SVT + TVU
STU = STV + UTV
So,
SVT = SVU  TVU
UTV = STU  STV
Since SVU = STU and TVU = STV,
SVT = STU  STV = UTV