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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 89 · 40 sums
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The method (Inside 180, outside the sum): Angle sum: ∠A + ∠B + ∠C = 180°. Exterior angle = sum of the two interior opposite angles. Right-angled triangle: longest side² = side² + side² (3, 4, 5 and 5, 12, 13 are famous sets). Sides can make a triangle only if the two shorter sides add up to more than the longest side.

NameDateTime takenScore ___ / 40
  1. 1.The two interior opposite angles of a triangle are 39° and 29°. What is the exterior angle (in degrees)?
  2. 2.Can a triangle have sides of 14 cm, 4 cm and 9 cm? (a) Yes (b) No
  3. 3.In triangle ABC, angle A = 24° and angle B = 100°. What is angle C (in degrees)?
  4. 4.Can a triangle have sides of 10 cm, 5 cm and 10 cm? (a) No (b) Yes
  5. 5.In a right-angled triangle, one of the other two angles is 54°. What is the third angle (in degrees)?
  6. 6.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  7. 7.In triangle ABC, angle A = 47° and angle B = 61°. What is angle C (in degrees)?
  8. 8.The two interior opposite angles of a triangle are 66° and 61°. What is the exterior angle (in degrees)?
  9. 9.In an isosceles triangle, the two equal angles are 62° each. What is the third angle (in degrees)?
  10. 10.The longest side of a right-angled triangle is 17 cm and one of the other sides is 8 cm. How long is the third side (in cm)?
  11. 11.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  12. 12.The longest side of a right-angled triangle is 25 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  13. 13.In triangle ABC, angle A = 31° and angle B = 87°. What is angle C (in degrees)?
  14. 14.An exterior angle of a triangle is 129°. One of its two interior opposite angles is 68°. What is the other one (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 34°. What is the third angle (in degrees)?
  16. 16.In triangle ABC, angle A = 61° and angle B = 69°. What is angle C (in degrees)?
  17. 17.In an isosceles triangle, the angle between the two equal sides is 96°. What is each of the other two angles (in degrees)?
  18. 18.The two shorter sides of a right-angled triangle are 5 cm and 12 cm. How long is the longest side (in cm)?
  19. 19.In a right-angled triangle, one of the other two angles is 22°. What is the third angle (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  21. 21.The two shorter sides of a right-angled triangle are 20 cm and 15 cm. How long is the longest side (in cm)?
  22. 22.In an isosceles triangle, the angle between the two equal sides is 42°. What is each of the other two angles (in degrees)?
  23. 23.The longest side of a right-angled triangle is 25 cm and one of the other sides is 7 cm. How long is the third side (in cm)?
  24. 24.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  25. 25.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  26. 26.In a right-angled triangle, one of the other two angles is 71°. What is the third angle (in degrees)?
  27. 27.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  28. 28.An exterior angle of a triangle is 124°. One of its two interior opposite angles is 66°. What is the other one (in degrees)?
  29. 29.The longest side of a right-angled triangle is 13 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  30. 30.In a right-angled triangle, one of the other two angles is 39°. What is the third angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 26°. What is the third angle (in degrees)?
  32. 32.The two interior opposite angles of a triangle are 34° and 21°. What is the exterior angle (in degrees)?
  33. 33.An exterior angle of a triangle is 112°. One of its two interior opposite angles is 48°. What is the other one (in degrees)?
  34. 34.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  36. 36.Can a triangle have sides of 12 cm, 10 cm and 2 cm? (a) No (b) Yes
  37. 37.The two interior opposite angles of a triangle are 40° and 56°. What is the exterior angle (in degrees)?
  38. 38.The longest side of a right-angled triangle is 17 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  39. 39.An exterior angle of a triangle is 132°. One of its two interior opposite angles is 66°. What is the other one (in degrees)?
  40. 40.In a right-angled triangle, one of the other two angles is 72°. What is the third angle (in degrees)?

Answer key

  1. 68
  2. No
  3. 56
  4. Yes
  5. 36
  6. 22
  7. 72
  8. 127
  9. 56
  10. 15
  11. 90
  12. 7
  13. 62
  14. 61
  15. 56
  16. 50
  17. 42
  18. 13
  19. 68
  20. 65
  21. 25
  22. 69
  23. 24
  24. 120
  25. 70
  26. 19
  27. 70
  28. 58
  29. 5
  30. 51
  31. 64
  32. 55
  33. 64
  34. 72
  35. 69
  36. No
  37. 96
  38. 8
  39. 66
  40. 18

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