4.5: Isosceles and Equilateral Triangles Objective: To use and apply properties of isosceles and equilateral triangles.
Isosceles Triangles 2 congruent legs Third side is the base The 2 congruent sides form the vertex angle The other 2 angles are the base angles. Vertex Angle Base Angles Legs BASE
Isosceles Triangle Theorem If a triangle is isosceles, then the base angles are congruent. C A B
Converse of Isosceles Triangle Theorem If 2 angles of a triangle are congruent, then the sides opposite the angles are congruent. (Therefore, it’s an isosceles triangle) C A B
THEOREM: The bisector of the vertex angle of an isosceles triangle is the perpendicular bisector of the base. C AB bisects D
Find the value of the variables. 54⁰ x y
Find the values of the variables y° 63° x° 4 cm z x° 65°
How do we know that triangle RST is isosceles? R U T W S V
How do you know is isosceles? A CB
Corollary: A statement that immediately follows a theorem. Corollary to the Isosceles Triangle Theorem: If a triangle is equilateral, then it is equiangular Corollary to converse of Isosceles Triangle Theorem : If a triangle is equiangular, then it is equilateral. A B C B A C
Find the values of the variables x 60 The perimeter is 54 cm. NOT DRAWN TO SCALE!! y° 60° x°
Find the value of the variables. The perimeter is 45 ft. (4y) (2x +1)