Theorem
In an isosceles triangle, the angles at the base are equal.
Evidence.
Let ABC be an isosceles triangle with base AB.
The triangle ACB is equal to the triangle BCA by the first sign of equality of the triangles. AC = BC, CB = CA, ∠ C = C. Therefore, ∠ A = ∠ B. The theorem is proved. |
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Planometry
Terms: Planometry