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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 617 · 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 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)?
  2. 2.The two interior opposite angles of a triangle are 61° and 70°. What is the exterior angle (in degrees)?
  3. 3.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  4. 4.In triangle ABC, angle A = 36° and angle B = 21°. What is angle C (in degrees)?
  5. 5.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  6. 6.Can a triangle have sides of 12 cm, 23 cm and 10 cm? (a) No (b) Yes
  7. 7.An exterior angle of a triangle is 76°. One of its two interior opposite angles is 33°. What is the other one (in degrees)?
  8. 8.An exterior angle of a triangle is 79°. One of its two interior opposite angles is 28°. What is the other one (in degrees)?
  9. 9.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  10. 10.In an isosceles triangle, the two equal angles are 76° each. What is the third angle (in degrees)?
  11. 11.An exterior angle of a triangle is 78°. One of its two interior opposite angles is 41°. What is the other one (in degrees)?
  12. 12.In an isosceles triangle, the angle between the two equal sides is 88°. What is each of the other two angles (in degrees)?
  13. 13.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  14. 14.In triangle ABC, angle A = 34° and angle B = 20°. What is angle C (in degrees)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 158°. What is each of the other two angles (in degrees)?
  16. 16.In a right-angled triangle, one of the other two angles is 13°. What is the third angle (in degrees)?
  17. 17.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  18. 18.In a right-angled triangle, one of the other two angles is 75°. What is the third angle (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  20. 20.In an isosceles triangle, the angle between the two equal sides is 22°. What is each of the other two angles (in degrees)?
  21. 21.In triangle ABC, angle A = 98° and angle B = 47°. What is angle C (in degrees)?
  22. 22.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  23. 23.In an isosceles triangle, the two equal angles are 85° each. What is the third angle (in degrees)?
  24. 24.An exterior angle of a triangle is 118°. One of its two interior opposite angles is 70°. What is the other one (in degrees)?
  25. 25.In a right-angled triangle, one of the other two angles is 27°. What is the third angle (in degrees)?
  26. 26.In triangle ABC, angle A = 63° and angle B = 81°. What is angle C (in degrees)?
  27. 27.Can a triangle have sides of 10 cm, 12 cm and 3 cm? (a) No (b) Yes
  28. 28.An exterior angle of a triangle is 134°. One of its two interior opposite angles is 80°. What is the other one (in degrees)?
  29. 29.Can a triangle have sides of 9 cm, 2 cm and 14 cm? (a) Yes (b) No
  30. 30.Can a triangle have sides of 12 cm, 26 cm and 10 cm? (a) No (b) Yes
  31. 31.In a right-angled triangle, one of the other two angles is 58°. What is the third angle (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 31°. What is the third angle (in degrees)?
  33. 33.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  34. 34.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  35. 35.In triangle ABC, angle A = 93° and angle B = 33°. What is angle C (in degrees)?
  36. 36.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  37. 37.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  38. 38.An exterior angle of a triangle is 58°. One of its two interior opposite angles is 23°. What is the other one (in degrees)?
  39. 39.An exterior angle of a triangle is 71°. One of its two interior opposite angles is 36°. What is the other one (in degrees)?
  40. 40.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?

Answer key

  1. 24
  2. 131
  3. 100
  4. 123
  5. 74
  6. No
  7. 43
  8. 51
  9. 40
  10. 28
  11. 37
  12. 46
  13. 72
  14. 126
  15. 11
  16. 77
  17. 20
  18. 15
  19. 78
  20. 79
  21. 35
  22. 25
  23. 10
  24. 48
  25. 63
  26. 36
  27. Yes
  28. 54
  29. No
  30. No
  31. 32
  32. 59
  33. 70
  34. 25
  35. 54
  36. 17
  37. 120
  38. 35
  39. 35
  40. 30

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