Sum of the Angles in a Triangle

Sum of the Angles in a Triangle

7.11C: write and solve equations using geometric concepts, including sum of the angles in a triangle and angle relationships

Classify Triangles

by ANGLES

Classify Triangles

by SIDES

Multiple Select

Which of the following classify triangles by their angles?

• Scalene

• Right

• Isosceles

• Acute

• Obtuse

Multiple Select

Which of the following classify triangles by their sides?

• Scalene

• Right

• Isosceles

• Acute

• Equilateral

Multiple Choice

A triangle with three acute angles and three congruent sides.

• Acute Obtuse Triangle

• Acute Isosceles Triangle

• Acute Equilateral Triangle

• Acute Scalene

Multiple Choice

A triangle with one right angle and no congruent sides.

• Acute Isosceles Triangle

• Right Isosceles Triangle

• Right Scalene Triangle

• Acute Scalene Triangle

Multiple Choice

Classify the marked triangle by its angles and by its sides.

• Acute Isosceles

• Right Equilateral

• Acute Equilateral

• Obtuse Isosceles

Multiple Choice

Classify the marked triangle by its angles and by its sides.

• Acute Isosceles

• Right Equilateral

• Acute Equilateral

• Acute Scalene

Multiple Choice

Classify the marked triangle by its angles and by its sides.

• Acute Equilateral

• Obtuse Isosceles

• Acute Isosceles

• Obtuse Equilateral

Angles in a Triangle

The sum of the measures of the angles of a triangle is 180 $\degree$ .

Example 1:

• Write and solve the equation to determine the value of x.

• (write an equation first)

• (solve the equation to determine the value of x)

• <a + <b + <c =180 **Remember that adding all 3 angles will equal to 180 degrees.

• Use "river bridge" to solve the equation to determine x

Example 2:

• Write and solve the equation to determine the measures of the missing angles.

• (write an equation first)

• (solve the equation to determine the value of x)

• <a + <b + <c =180 **Remember that adding all 3 angles will equal to 180 degrees.

• Use "river bridge" to solve the equation to determine x

• Plug-in the x to find the measures of the missing angles

Example 3:

• In triangle ABC, m<A=25, m<B=107, m<C=(3x). Write and solve an equation to determine the value of x.

• (write an equation first)

• (solve the equation to determine the value of x)

• <a + <b + <c =180 **Remember that adding all 3 angles will equal to 180 degrees.

• Use "river bridge" to solve the equation to determine x

Multiple Choice

The measures of two angles in a triangle are shown in the diagram. Which equation can be used to find the value of x?

• 48 + 2x = 180

• 2(48) + x = 180

• 48 + 2x = 360

• 2(48) + x = 360

Multiple Choice

The measures of two angles in a triangle are shown in the diagram. What is the measure of < x?

• 88⁰

• 157⁰

• 268⁰

• 67⁰

Multiple Choice

Find the measures of < A and < C in triangle ABC shown.

• 60 and 120

• 25 and 35

• 120 and 180

• 30 and 30

Multiple Choice

Can the measures of the angles of a triangle be 40°, 70°, and 60°?

• YES

• NO

Poll

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