Download Find Angle Measures

You solved equations by adding or subtracting.
(Lesson 4–3)
• Find the missing angle measure of a
triangle.
• Classify triangles by properties and
attributes.
• line segment
• triangle
• vertex
• congruent
Find Angle Measures
Find the value of x in ΔDEF.
Write an equation.
100 + 33 + x = 180
133 + x = 180
Substitution
Simplify.
133 – 133 + x = 180 – 133 Subtract 133 from
each side.
x = 47
Answer: x is 47, so mF = 47°.
Simplify.
Find the value of x in ΔMNO.
A. 57
B. 123
C. 139
D. 303
Use Algebra to Find Angle Measures
ALGEBRA The measures of the angles of a triangle
are 2x, x + 25, and x – 5. What are the measures of
the angles?
The sum of the angle measures is 180.
2x + (x +25) + (x + -5) = 180
4x +20 = 180
- 20
-20
4x = 160
Write the equation.
Combine like terms.
Subtract.
Simplify.
Divide each side by 4.
x = 40
Simplify.
Use Algebra to Find Angle Measures
Substitute 40 for x in each expression.
2x = 2(40) = 80
x + 25 = 40 + 25 = 65
x - 5 = 40 - 5 = 35
Answer: The measures of the angles are 80°, 65°,
and 35°.
Classify Triangles
A. Classify the triangle below by its angles and by
its sides.
Angles: The triangle has an obtuse angle.
Sides: The triangle has no congruent sides.
Answer: The triangle is an obtuse scalene triangle.
Classify Triangles
B. Classify the triangle by its
angles and by its sides.
Angles: The triangle has a right angle.
Sides: The triangle has two congruent sides.
Answer: The triangle is a right isosceles triangle.
A. Classify the triangle
by its angles and by its
sides.
A. right scalene
B. obtuse scalene
C. obtuse isoceles
D. acute equilateral
B. Classify the triangle by its
angles and by its sides.
A. right isoceles
B. obtuse isoceles
C. obtuse scalene
D. acute equilateral