Which of these is a theorem, not an axiom?

  1. The base angles of an isosceles triangle are equal.
  2. Things equal to the same thing are equal to each other.
  3. A straight line can be drawn between any two points.
  4. All right angles are equal.
Answer

A) The base angles of an isosceles triangle are equal.

The isosceles-triangle property is proved; the others are Euclid's axioms or postulates. SLO M-09-B-14 · Knowledge

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