Guided Notes – Lesson 6.5
Geometry
Name __________________________________
Definition – The ______________ sides of a trapezoid are its bases. The _________________ sides are its legs.
Two angles that share a _________ of a trapezoid are base angles of the trapezoid.
* Copy definition of base angles of a trapezoid onto your pink definitions sheet *
Theorem 6-15: The base angles of an isosceles trapezoid are ___________________.
* Copy theorem 6-15 onto your pink theorem sheet *
Therefore the two angles that share a leg are _____________________________.
Examples: Find the values of the missing angles.
1.
2.
 1 ________
 2 _______
3.
 1 _______
 2 _______
 1 ________
4. The spiders web to the right is formed by a layer of congruent isosceles triangles followed
by layers of congruent isosceles trapezoids. Find the measures of the angles in ABDC.
Hint: To begin, remember the angles of a circle add up to 360°. Decimal answers are OK!
DAB _________ ABC ________ BCD ___________ CDA ___________
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Examples: Find the values of the variables in the following figures.
5.
6.
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7.
Theorem 6-16: The ________________ of an isosceles trapezoid are ______________________.
* Copy theorem 6-16 onto your pink theorem sheet *
Proof of Theorem 6-16
Given: ABCD is an isosceles trapezoid
Prove: AC  DB
Statements
1. ABCD is an isosceles trapezoid
 2. AB  DC
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Reasons
1.
2.
3. ABC  DCB
3.
4. BC  BC
4.
5. ABC  DCB
5.
6. AC  DB
6.
 2 _______
Example: Find the value of x and find AC and BD.
AC = 10x – 60
BD = 2x + 100
Theorem 6-17: The ________________ of a kite are __________________________.
* Copy theorem 6-17 onto your pink theorem sheet *
Examples: Find the values of the missing angles.
1.
 1 ________
2.
 2 _______
 1 ________
3.
 2 _______
 1 _______  2 _______  3 ______
Examples: Find the values of the variables in the following figures.
4.
5.
6.
* Note: We will not do Defn of Midsegment of a Trapezoid or Theorem 6-18 so you can cross them out on your salmon sheets *
Homework 6.5: p.338 #1-7, 8-22 even, 23-27 odd
THT: Due Monday!!!