Section 4.5 isosceles & equilateral triangles Geometry
Isosceles Triangle Legs are congruent Vertex Angle Legs Base Angles
Theorem 4-3 (Isosceles Triangle Thm): If two sides of a triangle are congruent, then the angles opposite those sides are congruent. c b a
Theorem 4-4 (Converse of Isosceles Triangle Thm): If two angles of a triangle are congruent, then the sides opposite the angles are congruent.
Theorem 4-5 The bisector of the vertex angle of an isosceles triangle is the perpendicular bisector of the base. A B C
Ex. 2) Find the values of x and y. M y° x° 63° L N
Corollary: a statement that follows immediately from a theorem Corollary to Thm 4-3: If a triangle is equilateral, then it is equiangular. Corollary to Thm 4-4: If a triangle is equiangular, then it is equilateral.
Ex. 3) If find A B C M
Ex. 4) A If find B C M
Ex. 5) A If and find x. B C M
Ex. 6) Find the missing angles and sides.