Isosceles_Triangle_has_Two_Equal_Angles
Disprovedisosceles-trianglesproofwiki
In isosceles triangles, the angles at the base are equal to each other. Also, if the equal straight lines are extended, the angles under the base will also be equal to each other.
Preamble
import Mathlib.Analysis.Complex.Basic import Mathlib.Analysis.SpecialFunctions.Trigonometric.Basic
Formal statement
import Mathlib.Analysis.Complex.Basic import Mathlib.Analysis.SpecialFunctions.Trigonometric.Basic theorem Isosceles_Triangle_has_Two_Equal_Angles (a b c A B C : ℝ) (hab : a = b) (hA : Real.sin A ≠ 0) (hB : Real.sin B ≠ 0) (hlaw : a / Real.sin A = b / Real.sin B) : A = B := by sorry
Source