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Type of Class:
Standard
High School Geometry
Related VA SOL:
G.5
Time Frame:
Ninety minute block
class
Objectives:
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Students will know how to prove two right triangles are similar.
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Students will know how to prove two right triangles are congruent.
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Students will use practical problems to prove right triangles are
similar and congruent.
Materials:
- Chalkboard
- Graph paper
- Ruler
- Protractor
Procedures:
1)
Definitions
a)
Geometric mean: For any two positive numbers a and b, the geometric mean of
a and b is the positive number x such that .
b)
Corollary 1: The length of the altitude of the hypotenuse of a right
triangle is the geometric mean of the lengths of the sub-segments of the
hypotenuse.
c)
Corollary 2: The altitude of the hypotenuse of a right triangle intersects
it so that the length of each leg is the geometric mean of the length of its
adjacent segment of the hypotenuse and the length of the entire hypotenuse.
2)
Similarity in right triangles:


3)
Congruence in right triangles
a)
If the hypotenuse and a leg of one right triangle are congruent to the
hypotenuse and leg of another right triangle, then the triangles are congruent
by the
Hypotenuse-Leg Theorem (HL).

b)
Example to be done in groups while the teacher walks around and makes
sure students are on the right path:
i)
Each group to put answer on board upon completion
ii)
Graph the points E(-1,-1), F(-2,-6), G(-4,-4), D(-6,-2)
(1)
Connect the points with segments
iii)
Find the slopes of the segments DG, GF, and GE
iv)
Use the answer from above to describe

v)
Use the distance formula to find the measures DE and FE
vi)
Write a paragraph to prove EGD EGF
Assessment:
Assigned homework to be started in class if time permits
Suggestions/Comments:
This lesson would be more effective if it were to take place
immediately following the lesson on proving congruency and similarity in
triangles. With this prior information, the students are already familiar with
techniques to prove triangles and the lesson should flow better.
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