Isosceles and Equilateral
Triangles
Geometry 4-5
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Legs
Base Angles
Vertex Angle
Base
Isosceles Triangle Terms
Parts of Isosceles Triangle
• What can we learn from the
symmetry of an isosceles
triangle?
Isosceles Conjectures
• Supplies
Printer Paper
Compass
Straight Edge
Protractor
Scissors
Investigation
• Everyone construct a large
isosceles triangle on a piece of
paper.
• Cut it out
• Label it ARK, with K as the
vertex angle
Investigation
• Fold the triangle so that angles
A and R are touching, and angle
K is bisected.
• Unfold and label the end of the
fold line X
• Compare angles A and R
Investigation
Theorem
• How would you word the converse of
the previous Theorem?
Is the converse true?
Investigation
Theorem
• Measure KXA and KXR
• Compare lines AX and RX
• Conclusions?
Investigation
Theorem
• On another piece of paper
• Construct a large equilateral triangle (using a
compass)
• Measure all of the angles
Investigation
• How could we show this as a proof, without
measuring?
Proof
Proof
Corollary means that the
conclusion is drawn as one more
step to a previous theorem
Corollary
Corollary
Practice Problems
Practice Problems
Practice Problems
Practice Problems
Practice Problems
Practice Problems
Practice Problems
Practice Problems
Practice Problems
Practice Problems
Practice Problems
• Pages 213 – 216
• 1, 7 – 12, 24, 25, 29, 50 – 52
Homework
• Pages 213 – 216
• 1, 7 – 12, 24, 25, 29, 33, 50 – 52
Honors Homework