Name________________________

SUM OF THE INTERIOR ANGLES OF A TRIANGLE  #2-KEY

Directions:  Solve for x in each of the triangles below.  The Triangle Sum Theorem states that the interior angles of a triangle always add up to 180̊	.  Your first step should be to set up an equation where the sum of the angles adds up to 180̊.  Solve the equation for x, then plug that value back in to the expressions to find the measure of the missing angles.	

C

C

B

A

C

x

x

5x

70̊

6x

1)              	         	               2)                                              3)                                          4)  

 

3x

A

A

A

B

60̊

x+50

x+10

70̊

C

B

B

4x

50̊

             x = __30___                             x = _ 60___                             x = __10___                           x = _  12_  _

     _  90̊____                      _ 70̊__ _                      _  60̊__                       _   62̊___ 

     _  30̊____                     _  60̊__ _                      _  50̊__                       __ 48̊_  _ 

A

A

B

A

B

B

3x+5

3x+50

60̊

5)              	         	                6)                                              7)                                          8)  

5x

2x

40̊

3x

2x+20

77̊

C

B

C

C

3x-20

2x

C

A

             x = __15___                             x =    _ 30___                             x = __ 8___                           x = _  22_  _

     _  75̊____                      _ 60̊__ _                      _  74̊__                       _   44̊___ 

     _  45̊____                     _  80̊__ _                      _  29̊__                       __ 46̊_  _ 

A

C

A

A

29̊

x

B

2x

37̊

9)                                           10)                                             11)                                           12)  

2x+15

B

7x

2x

80̊

2x

C

B

A

C

B

4x+30

2x+30

72̊

C

             x = __32___                             x =    _ 26___                             x = __ 11___                           x = _  25_  _

     _  79̊____                      _ 26̊__ _                      _  77̊__                       _   50̊___ 

     _  64̊____                     _  82̊__ _                      _  74̊__                       __ 50̊_  _ 

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