(Aren't two column proofs the best? I used to shred a paper when a question asked me to write proof, back in Geometry class)
So I assume the check mark mean you got that part correct. For the first statement, it should be correct, and I don't know why it isn't marked right.
Step three is basically the same exact thing as step two, so perhaps, don't add that step.
For me, the question is asking something that is so simple, that it could be solved with basic LOGIC.
However, since its asking us to write a "proof," here's my "fabulous" two column proof:
<ABC = <DEF - Given
<GHI = <DEF - Given
<ABC = GHI - Transitive property.
Overall, I have really negative feelings toward proofs because most of the time, the use of all these stupid theorems and postulates is dumb.
