Download Lesson 3.4

Lesson 3.4
TOPIC/Objective: To use angles to tell whether triangles
are similar.
Essential Question: How can you use angles to tell if triangles are similar.
Example:
The triangles have two
pairs of congruent
angles.
The 3rd angle in each triangle must be 55⁰, therefore the triangles
are similar.
Example:
Solve for x and y
in each triangle
63 + 63 + y = 180
126 + y = 180
y = 54
Both triangles have angles of 54, 63, 63
Similar
Example:
38 + y + 90 = 180
128 + y = 180
y = 52
90, 42, 48
38, 52, 90
Only one angle is the same. Not Similar
Example:
You place a mirror on the ground 6
feet from the lamppost. You move
back 3 feet and see the top of the
lamppost in the mirror. You are 5 feet
tall. What is the height of the
lamppost?
5ft
3ft
The triangles are similar because
two angles are the same,
making all angles the same.
The light pole is 10 ft. tall
5 𝑥
=
3 6
3x = 30
X = 10
6ft