One is given the following information:
- Triangle (ABC) is an isosceles triangle (meaning two of its sides are congruent
- Side (AB = AC)
One property of an isosceles triangle is the base angles theorem. This states that in an isosceles triangle, the two angles that are opposite the congruent sides are also congruent. Applying this theorem here, one can state the following:
The sum of angle measures in a triangle is (180) degrees. One can apply this here by stating the following:
Substitute in the proved information: express angle (<C) in terms of angle (<B).
Simplify, combine like terms.
Inverse operations: solve for angle (<B)
Simplify,
Thus, one has proven that the statement (
) is true.
Please note, this proof can be typed in a statement-reason format, where the bolded part of the written words above the statement is the reason.