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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 677 · 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.An exterior angle of a triangle is 115°. One of its two interior opposite angles is 40°. What is the other one (in degrees)?
  2. 2.An exterior angle of a triangle is 51°. One of its two interior opposite angles is 20°. What is the other one (in degrees)?
  3. 3.In a right-angled triangle, one of the other two angles is 23°. What is the third angle (in degrees)?
  4. 4.Can a triangle have sides of 16 cm, 7 cm and 6 cm? (a) Yes (b) No
  5. 5.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  6. 6.The two interior opposite angles of a triangle are 65° and 40°. What is the exterior angle (in degrees)?
  7. 7.The two interior opposite angles of a triangle are 38° and 43°. What is the exterior angle (in degrees)?
  8. 8.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  9. 9.In a right-angled triangle, one of the other two angles is 33°. What is the third angle (in degrees)?
  10. 10.In triangle ABC, angle A = 99° and angle B = 43°. What is angle C (in degrees)?
  11. 11.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  12. 12.In triangle ABC, angle A = 86° and angle B = 51°. What is angle C (in degrees)?
  13. 13.In triangle ABC, angle A = 97° and angle B = 36°. What is angle C (in degrees)?
  14. 14.The two shorter sides of a right-angled triangle are 15 cm and 20 cm. How long is the longest side (in cm)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 100°. What is each of the other two angles (in degrees)?
  16. 16.In triangle ABC, angle A = 77° and angle B = 80°. What is angle C (in degrees)?
  17. 17.An exterior angle of a triangle is 89°. One of its two interior opposite angles is 41°. What is the other one (in degrees)?
  18. 18.An exterior angle of a triangle is 70°. One of its two interior opposite angles is 35°. What is the other one (in degrees)?
  19. 19.Can a triangle have sides of 4 cm, 10 cm and 12 cm? (a) Yes (b) No
  20. 20.The two interior opposite angles of a triangle are 54° and 73°. What is the exterior angle (in degrees)?
  21. 21.In triangle ABC, angle A = 63° and angle B = 24°. What is angle C (in degrees)?
  22. 22.The two interior opposite angles of a triangle are 74° and 30°. What is the exterior angle (in degrees)?
  23. 23.An exterior angle of a triangle is 93°. One of its two interior opposite angles is 52°. What is the other one (in degrees)?
  24. 24.In an isosceles triangle, the angle between the two equal sides is 42°. What is each of the other two angles (in degrees)?
  25. 25.In a right-angled triangle, one of the other two angles is 79°. What is the third angle (in degrees)?
  26. 26.The two interior opposite angles of a triangle are 34° and 61°. What is the exterior angle (in degrees)?
  27. 27.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  28. 28.The longest side of a right-angled triangle is 15 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  29. 29.In an isosceles triangle, the two equal angles are 77° each. What is the third angle (in degrees)?
  30. 30.In an isosceles triangle, the two equal angles are 74° each. What is the third angle (in degrees)?
  31. 31.Can a triangle have sides of 7 cm, 8 cm and 3 cm? (a) Yes (b) No
  32. 32.An exterior angle of a triangle is 67°. One of its two interior opposite angles is 31°. What is the other one (in degrees)?
  33. 33.An exterior angle of a triangle is 156°. One of its two interior opposite angles is 79°. What is the other one (in degrees)?
  34. 34.An exterior angle of a triangle is 75°. One of its two interior opposite angles is 46°. What is the other one (in degrees)?
  35. 35.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  36. 36.Can a triangle have sides of 19 cm, 8 cm and 10 cm? (a) No (b) Yes
  37. 37.In a right-angled triangle, one of the other two angles is 61°. What is the third angle (in degrees)?
  38. 38.The longest side of a right-angled triangle is 15 cm and one of the other sides is 9 cm. How long is the third side (in cm)?
  39. 39.In a right-angled triangle, one of the other two angles is 77°. What is the third angle (in degrees)?
  40. 40.In an isosceles triangle, the two equal angles are 43° each. What is the third angle (in degrees)?

Answer key

  1. 75
  2. 31
  3. 67
  4. No
  5. 72
  6. 105
  7. 81
  8. 90
  9. 57
  10. 38
  11. 17
  12. 43
  13. 47
  14. 25
  15. 40
  16. 23
  17. 48
  18. 35
  19. Yes
  20. 127
  21. 93
  22. 104
  23. 41
  24. 69
  25. 11
  26. 95
  27. 62
  28. 9
  29. 26
  30. 32
  31. Yes
  32. 36
  33. 77
  34. 29
  35. 120
  36. No
  37. 29
  38. 12
  39. 13
  40. 94

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