1. Triangles
© T Madas

2. ? ? Isosceles Equilateral Scalene Acute Does not exist Obtuse
Right angled
Does not exist
© T Madas

3. The angles in a triangle add up to 180 degrees
© T Madas

4. The angles in a triangle add up to 180°
© T Madas

5. The angles in a triangle add up to 180°
© T Madas

6. The angles in a triangle add up to 180°
© T Madas

7. Practice
Angle Calculations
with Triangles
© T Madas

8. Calculations with Triangles
60°
100°
45°
45°
35°
70°
50°
80°
55°
45°
65°
25°
65°
70°
25°
30°
55°
120°
115°
35°
35°
75°
50°
© T Madas

9. Calculations with Triangles
70°
104°
48°
43°
33°
65°
45°
80°
52°
47°
61°
29°
62°
71°
24°
33°
52°
117°
109°
39°
38°
77°
51°
© T Madas

10. Calculations with Triangles
80°
101°
47°
43°
36°
60°
40°
80°
53°
48°
64°
26°
61°
71°
23°
32°
52°
117°
110°
40°
38°
78°
50°
© T Madas

11. Calculations with Isosceles Triangles
50°
40°
70°
40°
100°
55°
55°
70°
70°
65°
65°
40°
80°
110°
45°
45°
20°
80°
35°
35°
© T Madas

12. Quick Test on
Angle Calculations
with Triangles
© T Madas

13. Calculations with Triangles
60°
100°
45°
45°
35°
70°
50°
80°
55°
45°
65°
25°
65°
70°
25°
30°
55°
120°
115°
35°
35°
75°
50°
© T Madas

14. Calculations with Triangles
70°
104°
48°
43°
33°
65°
45°
80°
52°
47°
61°
29°
62°
71°
24°
33°
52°
117°
109°
39°
38°
77°
51°
© T Madas

15. Calculations with Triangles
80°
101°
47°
43°
36°
60°
40°
80°
53°
48°
64°
26°
61°
71°
23°
32°
52°
117°
110°
40°
38°
78°
50°
© T Madas

16. Calculations with Isosceles Triangles
50°
40°
70°
40°
100°
55°
55°
70°
70°
65°
65°
40°
80°
110°
45°
45°
20°
80°
35°
35°
© T Madas

17. © T Madas

18. An isosceles triangle ABC is drawn below, with the points A and B fixed and point C free to move.
Mark on the grid another position for point C, so that triangle is still isosceles. 6 5 4 3 2 1 C A B
© T Madas

19. An isosceles triangle ABC is drawn below, with the points A and B fixed and point C free to move.
Mark on the grid another position for point C, so that triangle is still isosceles. 6 5 4 3 2 1 C A B
© T Madas

20. An isosceles triangle ABC is drawn below, with the points A and B fixed and point C free to move.
Mark on the grid another position for point C, so that triangle is still isosceles. 6 5 4 3 2 1 A B
© T Madas

21. An isosceles triangle ABC is drawn below, with the points A and B fixed and point C free to move.
Mark on the grid another position for point C, so that triangle is still isosceles. 6 5 4 3 2 1 C A B
© T Madas

22. An isosceles triangle ABC is drawn below, with the points A and B fixed and point C free to move.
Mark on the grid another position for point C, so that triangle is still isosceles. 6 5 4 3 2 1 C A B
© T Madas

23. An isosceles triangle ABC is drawn below, with the points A and B fixed and point C free to move.
Mark on the grid another position for point C, so that triangle is still isosceles. 6 5 4 3 2 1 C A B
Mark on the grid another position for point C, so that triangle is isosceles and right angled.
© T Madas

24. An isosceles triangle ABC is drawn below, with the points A and B fixed and point C free to move.
Mark on the grid another position for point C, so that triangle is still isosceles. 6 5 4 3 2 1 C A B
Mark on the grid another position for point C, so that triangle is isosceles and right angled.
© T Madas

25. © T Madas

26. Calculate the angle marked as x.
69°
61°
21°
29°
50° x
© T Madas

27. © T Madas

28. Calculate the angle marked as x
20°
50°
130°
70°
30° x
© T Madas

29. © T Madas

30. Calculate the angle marked as x.
49°
41°
49° x
© T Madas

31. © T Madas

32. Calculate the three angles of the triangle
70°
140°
40°
70°
Calculate the angle marked with x
55°
110° x
70°
55°
© T Madas

33. © T Madas

34. Calculate the angle marked with x
292° x
68°
136°
44°
68°
© T Madas

35. © T Madas

36. Calculate the missing angles in each triangle
70°
50°
55°
55°
65°
65°
© T Madas

37. © T Madas

38. One of the angles of an isosceles triangle is 64°.
What are the sizes of the other two angles?
[You must show that there are 2 different possibilities]
1st possibility
2nd possibility
52°
64°
64°
64°
58°
58° 64
+ 64
128
180
– 128 52
180
– 64
116
116 ÷ 2 =
58°
© T Madas

39. © T Madas