Parallel Lines and Triangles

3.5 Triangle Angle Sum

be sure to write down notes as you go

​The interior angles in a triangle add up to 180 degrees.

Multiple Choice

The Triangle Angle Sum Theorem says that the interior angles in a triangle add up to _ degrees

• 90

• 360

• 180

• 270

​Let me check your work when you finish.

Multiple Choice

Find the measure of the ? angle

• 112

• 180

• 68

• 90

​Solve for x in the picture.

• ​set up an equation

• ​add the angles of the triangle together on one side

• ​put 180 on the other side

• ​solve your equation for x.

• ​let me check your work when you are done.

Multiple Choice

Which equation would let you solve for x in the triangle? 

• 6x+51=63

• 6x+51+63=180

• 6x+51+63=90

• 6x+63=51

​Write the equation to solve for x in the picture.

​Solve for x and let me check your answer when you are done.

​An exterior angle is formed by extending any one side of a triangle.

Multiple Choice

According to the Exterior Angle Theorem,  $$m\angle1=$$  

• $$m\angle2-m\angle3$$  

• 90

• 180

• $$m\angle2+m\angle3$$  

Multiple Choice

Use the Exterior Angle Theorem to find the equation to solve for x.

• x=86-63

• x+63+86=180

• x=63+86

• x+63+86=90

Multiple Choice

Use the Exterior Angle Theorem to solve for x.

• x=23

• x=149

• x=23

• x=-59

​All Done! You may now work on your practice!