Download Section 4.1 Day 2 Triangles and Angles

Week 3
Warm Up
State the number of sides:
1) Trapezoid
2) Parallelogram
11.01.11
Re 1
m∠x?
B
65⁰
A
58⁰
x⁰
C
58 + 65 + x = 180º
123 + x = 180
x = 180 - 123
x = 57º
Geometry
4.1 Day 2
Interior
Angles
I will classify triangles by their sides and angles.
The three original angles on the inside of the triangle.
Exterior
Angles
Adjacent to the interior angles.
Theorem
4.2
Exterior Angle Theorem
The measure of an exterior angle of a triangle is
equal to the sum of the measure of the two
nonadjacent interior angles.
B
1
A
C
m∠1 = m∠A + m∠B
B
65⁰
Ex 1
A
x⁰
( 2x + 10 )º = xº + 65º
2x + 10 = x + 65
2x - x + 10 = 65
x + 10 = 65
x = 65 - 10
x = 55
( 2x + 10 )⁰
C
2x + 10
2( 55 ) + 10
110 + 10
120º
Theorem
4.1
Triangle Sum Theorem
Don’t
Write!
The sum of the measure of the interior angles of a
triangle is 180⁰.
B
A
C
m∠A + m∠B + m∠C = 180⁰.
Theorem
4.1B
Corollary to the Triangle Sum Theorem
The acute angles of a right triangle are
complementary.
A
C
B
m∠A + m∠B = 90º
2x⁰
Ex 2
x⁰
90º = xº + 2xº
90 = 3x
15 = x
Algebra
Review
Writing
Equations
P( -2, -3 )
m=
y = mx + b
-3 = (
) ( -2 ) + b
-3 = 7 + b
-3 - 7 = + b
-10 = + b
y=
x - 10
Do: 1
what is the measure of the
exterior angle?
B
38⁰
( 10x + 9 )⁰
A
Assignment:
( 7x + 1 )⁰
Textbook Page 198, 10 - 32 evens.
C