Given: angle 1 is congruent to angle 2, Angle 2 is congruent to angle 3. Conclusion: angle 1 is congruent to angle 3.

Question

What steps are needed prior to the conclusion.  Its a trapezoid.

Answer 1

What you quote about equality of angles in pairs is known as the TRANSITIVE PROPERTY of EQUALITY, i.e. two things equal to another thing must be equal to one another.

 

This stated (given) set of facts may not be applicable to interior angles of a trapezoid, however.

Answer 2

Provided your steps are correct,

 

substitute 1 in the first step for 2 in the second step

 

angle 1 is congruent to angle 3 by substitution