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,

Therefore, corresponding angles

are congruent.

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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 ,

Then

By the ASA Theorem,




Now, put this into a two column proof.

Here is a drawing: