1. Triangles
© M. Tallman

2. Equilateral Triangle All three sides are congruent.
60°
4 inches
4 inches
60°
60°
4 inches
All three sides are congruent.
All three angles are also congruent, 60°.
Note: an equilateral triangle will always have three 60° angles, no matter what the size of the triangle.
© M. Tallman

3. Isosceles Triangle 40° 70° 70° Two sides are congruent.
4 inches
4 inches
Click here for a helpful trick.
70°
70°
3 inches
Two sides are congruent.
One side has a different length.
Two angles are congruent.
One angle is different.
© M. Tallman

4. All sides are different lengths. All angles are different.
Scalene Triangle
5.5 inches
3 inches
110°
50°
20°
7 inches
All sides are different lengths.
All angles are different.
© M. Tallman

5. Right Triangle Has one right angle. 90°
Note: It is not possible for a triangle to have more than one right angle.
© M. Tallman

6. All three angles are acute (less than 90°).
Acute Triangle
70°
50°
60°
All three angles are acute (less than 90°).
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7. One angle is obtuse (greater than 90 °) .
Obtuse Triangle
110°
One angle is obtuse (greater than 90 °) .
Note: It is not possible for a triangle to have more than one obtuse angle.
© M. Tallman

8. Equilateral, Isosceles, Scalene, Right, Acute, Obtuse.
Classify the Triangle
Equilateral, Isosceles, Scalene, Right, Acute, Obtuse.
c units Y° X°
a units Z°
b units
scalene
obtuse
© M. Tallman

9. Equilateral, Isosceles, Scalene, Right, Acute, Obtuse.
Classify the Triangle
Equilateral, Isosceles, Scalene, Right, Acute, Obtuse.
90° Y°
c units
a units X°
b units
right
scalene
© M. Tallman

10. Equilateral, Isosceles, Scalene, Right, Acute, Obtuse.
Classify the Triangle
Equilateral, Isosceles, Scalene, Right, Acute, Obtuse. X°
a units
a units X° X°
a units
equilateral
acute
© M. Tallman

11. Equilateral, Isosceles, Scalene, Right, Acute, Obtuse.
Classify the Triangle
Equilateral, Isosceles, Scalene, Right, Acute, Obtuse. X°
b units
b units Y° Y°
a units
isosceles
acute
© M. Tallman

12. Equilateral, Isosceles, Scalene, Right, Acute, Obtuse.
Classify the Triangle
Equilateral, Isosceles, Scalene, Right, Acute, Obtuse. X°
a units
b units X°
a units
right
isosceles
© M. Tallman

13. Equilateral, Isosceles, Scalene, Right, Acute, Obtuse.
Classify the Triangle
Equilateral, Isosceles, Scalene, Right, Acute, Obtuse. Y°
c units
a units Z° X°
b units
scalene
acute
© M. Tallman

14. Equilateral, Isosceles, Scalene, Right, Acute, Obtuse.
Classify the Triangle
Equilateral, Isosceles, Scalene, Right, Acute, Obtuse.
a units
a units Y° X° X°
b units
obtuse
isosceles
© M. Tallman

15. All Triangles Have 180° 20° 50° 20° 110° 50° 110° 20° 110° 50°
Although there are many different types of triangles, the sum of their angles will always equal 180°.
20°
Obtuse or Scalene
50°
20°
110°
50°
110°
20°
110°
50°
20° + 110° + 50° = 180°
© M. Tallman

16. All Triangles Have 180°
Although there are many different types of triangles, the sum of their angles will always equal 180°.
60°
Equilateral or Acute
60°
60°
60°
60°
60°
60°
60° + 60° + 60° = 180°
© M. Tallman

17. All Triangles Have 180°
Although there are many different types of triangles, the sum of their angles will always equal 180°.
55°
35°
55°
Right or Scalene
90°
35°
90°
55°
90°
35°
35° + 90° + 55° = 180°
© M. Tallman

18. All Triangles Have 180°
Although there are many different types of triangles, the sum of their angles will always equal 180°.
70°
40°
isosceles
40°
70°
70°
70°
40°
70°
40° + 70° + 70° = 180°
© M. Tallman

19. Find the missing angle. Then classify the triangle.
Mystery Angle
Find the missing angle. Then classify the triangle.
60°
equilateral
/acute
60°
60° ?
60° +
60° =
120°
180° -
120° =
60°
© M. Tallman

20. Find the missing angle. Then classify the triangle
Mystery Angle
Find the missing angle. Then classify the triangle
100° ?
obtuse
scalene
60°
20°
60° +
20° =
80°
180° -
80° =
100°
© M. Tallman

21. Find the missing angle. Then classify the triangle
Mystery Angle
Find the missing angle. Then classify the triangle
45°
right
isosceles
45° ?
90° +
45° =
135°
180° -
135° =
45°
© M. Tallman

22. Find the missing angle. Then classify the triangle
Mystery Angle
Find the missing angle. Then classify the triangle
65°
scalene
acute
70° ?
45°
65° +
45° =
110°
180° -
110° =
70°
© M. Tallman

23. Find the missing angle. Then classify the triangle
Mystery Angle
Find the missing angle. Then classify the triangle
20° ?
scalene
45°
obtuse
115°
115° +
45° =
160°
180° -
160° =
20°
© M. Tallman

24. Find the missing angle. Then classify the triangle
Mystery Angle
Find the missing angle. Then classify the triangle
40° ?
acute
isosceles
70°
70°
70° +
70° =
140°
180° -
140° =
40°
© M. Tallman

25. Find the missing angle. Then classify the triangle
Mystery Angle
Find the missing angle. Then classify the triangle
60°
right
scalene
30° ?
90° +
60° =
150°
180° -
150° =
30°
© M. Tallman

26. Find the missing angle. Then classify the triangle
Mystery Angle
Find the missing angle. Then classify the triangle
50° ?
right
40°
scalene
90° +
40° =
130°
180° -
130° =
50°
© M. Tallman

27. Find the missing angle. Then classify the triangle
Mystery Angle
Find the missing angle. Then classify the triangle
50° ?
obtuse
20°
scalene
110°
110° +
20° =
130°
180° -
130° =
50°
© M. Tallman

28. Find the missing angle. Then classify the triangle
Mystery Angle
Find the missing angle. Then classify the triangle
130°
obtuse
isosceles
25°
25° ?
25° +
130° =
155°
180° -
155° =
25°
© M. Tallman

29. Isosceles Triangle s o s O same same S S outcast
Can’t remember what an isosceles triangle is?
Try using this little trick!
The “sos” in isosceles can stand for same-outcast-same. O
same
same S S
Back to slide show
outcast
© M. Tallman