I am home-schooling and need help in presenting a two column proof of an Isosceles triangle. Need to present a two column proof for an Isosceles triangle (if the base angles of a triangle are congruent, then the triangle is Isosceles). Any help or direction to a good site would be appreciated.

Here are some good hints.

LEMMA:

By the SAS Postulate, \triangle CAB\equiv\triangle CBA

Therefore, corresponding angles \angle CAB \;\ \text{and} \;\ \angle CBA

are congruent. \therefore \angle{A}\equiv\angle{B}

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A triangle is isosceles iff the base angles are congruent.

In the light of the above, we only have to prove the converse.

If \angle{A}\equiv\angle{B},

Then \overline{AC}\equiv\overline{BC}

By the ASA Theorem, \triangle{CAB}\equiv\triangle{CBA}

\therefore \;\ \overline{AC}\equiv\overline{BC}


Now, put this into a two column proof.

Here is a drawing: