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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 541 · 40 sums
TalentJR

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.

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  1. 1.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  2. 2.In triangle ABC, angle A = 61° and angle B = 73°. What is angle C (in degrees)?
  3. 3.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)?
  4. 4.In triangle ABC, angle A = 46° and angle B = 38°. What is angle C (in degrees)?
  5. 5.In an isosceles triangle, the two equal angles are 53° each. What is the third angle (in degrees)?
  6. 6.In a right-angled triangle, one of the other two angles is 54°. What is the third angle (in degrees)?
  7. 7.The longest side of a right-angled triangle is 20 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  8. 8.In triangle ABC, angle A = 51° and angle B = 90°. What is angle C (in degrees)?
  9. 9.An exterior angle of a triangle is 138°. One of its two interior opposite angles is 69°. What is the other one (in degrees)?
  10. 10.In an isosceles triangle, the two equal angles are 27° each. What is the third angle (in degrees)?
  11. 11.In triangle ABC, angle A = 51° and angle B = 78°. What is angle C (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 56°. What is the third angle (in degrees)?
  13. 13.In a right-angled triangle, one of the other two angles is 47°. What is the third angle (in degrees)?
  14. 14.In triangle ABC, angle A = 86° and angle B = 35°. What is angle C (in degrees)?
  15. 15.The two interior opposite angles of a triangle are 74° and 40°. What is the exterior angle (in degrees)?
  16. 16.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  17. 17.In a right-angled triangle, one of the other two angles is 77°. What is the third angle (in degrees)?
  18. 18.In a right-angled triangle, one of the other two angles is 67°. What is the third angle (in degrees)?
  19. 19.In triangle ABC, angle A = 68° and angle B = 86°. What is angle C (in degrees)?
  20. 20.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  21. 21.In an isosceles triangle, the two equal angles are 72° each. What is the third angle (in degrees)?
  22. 22.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  23. 23.The two interior opposite angles of a triangle are 69° and 61°. What is the exterior angle (in degrees)?
  24. 24.Can a triangle have sides of 8 cm, 7 cm and 8 cm? (a) Yes (b) No
  25. 25.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  26. 26.Can a triangle have sides of 8 cm, 8 cm and 12 cm? (a) Yes (b) No
  27. 27.In a right-angled triangle, one of the other two angles is 50°. What is the third angle (in degrees)?
  28. 28.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  29. 29.Can a triangle have sides of 9 cm, 23 cm and 9 cm? (a) No (b) Yes
  30. 30.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  31. 31.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  32. 32.In triangle ABC, angle A = 69° and angle B = 69°. What is angle C (in degrees)?
  33. 33.In triangle ABC, angle A = 31° and angle B = 46°. What is angle C (in degrees)?
  34. 34.In an isosceles triangle, the angle between the two equal sides is 124°. What is each of the other two angles (in degrees)?
  35. 35.An exterior angle of a triangle is 138°. One of its two interior opposite angles is 66°. What is the other one (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 48°. What is the third angle (in degrees)?
  37. 37.In an isosceles triangle, the angle between the two equal sides is 134°. What is each of the other two angles (in degrees)?
  38. 38.The two shorter sides of a right-angled triangle are 20 cm and 15 cm. How long is the longest side (in cm)?
  39. 39.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 74° and 23°. What is the exterior angle (in degrees)?

Answer key

  1. 20
  2. 46
  3. 8
  4. 96
  5. 74
  6. 36
  7. 16
  8. 39
  9. 69
  10. 126
  11. 51
  12. 34
  13. 43
  14. 59
  15. 114
  16. 45
  17. 13
  18. 23
  19. 26
  20. 40
  21. 36
  22. 39
  23. 130
  24. Yes
  25. 100
  26. Yes
  27. 40
  28. 17
  29. No
  30. 35
  31. 72
  32. 42
  33. 103
  34. 28
  35. 72
  36. 42
  37. 23
  38. 25
  39. 36
  40. 97

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