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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 152 · 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.

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.In triangle ABC, angle A = 62° and angle B = 45°. What is angle C (in degrees)?
  3. 3.In an isosceles triangle, the angle between the two equal sides is 104°. What is each of the other two angles (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 75°. What is the third angle (in degrees)?
  5. 5.Can a triangle have sides of 11 cm, 5 cm and 12 cm? (a) Yes (b) No
  6. 6.In an isosceles triangle, the two equal angles are 62° each. What is the third angle (in degrees)?
  7. 7.Can a triangle have sides of 12 cm, 7 cm and 14 cm? (a) No (b) Yes
  8. 8.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)?
  9. 9.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  10. 10.In triangle ABC, angle A = 29° and angle B = 53°. What is angle C (in degrees)?
  11. 11.In triangle ABC, angle A = 60° and angle B = 20°. What is angle C (in degrees)?
  12. 12.In triangle ABC, angle A = 29° and angle B = 90°. What is angle C (in degrees)?
  13. 13.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  14. 14.The longest side of a right-angled triangle is 25 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  15. 15.The longest side of a right-angled triangle is 10 cm and one of the other sides is 6 cm. How long is the third side (in cm)?
  16. 16.In a right-angled triangle, one of the other two angles is 66°. What is the third angle (in degrees)?
  17. 17.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  18. 18.An exterior angle of a triangle is 101°. One of its two interior opposite angles is 64°. What is the other one (in degrees)?
  19. 19.In an isosceles triangle, the two equal angles are 72° each. What is the third angle (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 79°. What is the third angle (in degrees)?
  21. 21.Can a triangle have sides of 13 cm, 5 cm and 10 cm? (a) No (b) Yes
  22. 22.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  23. 23.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  24. 24.In triangle ABC, angle A = 92° and angle B = 36°. What is angle C (in degrees)?
  25. 25.In an isosceles triangle, the angle between the two equal sides is 78°. What is each of the other two angles (in degrees)?
  26. 26.In a right-angled triangle, one of the other two angles is 47°. What is the third angle (in degrees)?
  27. 27.In an isosceles triangle, the two equal angles are 31° each. What is the third angle (in degrees)?
  28. 28.The two interior opposite angles of a triangle are 38° and 37°. What is the exterior angle (in degrees)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 124°. What is each of the other two angles (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  31. 31.In triangle ABC, angle A = 92° and angle B = 43°. What is angle C (in degrees)?
  32. 32.In triangle ABC, angle A = 31° and angle B = 41°. What is angle C (in degrees)?
  33. 33.In an isosceles triangle, the two equal angles are 22° each. What is the third angle (in degrees)?
  34. 34.The two interior opposite angles of a triangle are 24° and 79°. What is the exterior angle (in degrees)?
  35. 35.In an isosceles triangle, the two equal angles are 65° each. What is the third angle (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 53°. What is the third angle (in degrees)?
  37. 37.Can a triangle have sides of 13 cm, 10 cm and 2 cm? (a) No (b) Yes
  38. 38.In triangle ABC, angle A = 39° and angle B = 38°. What is angle C (in degrees)?
  39. 39.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 74° and 61°. What is the exterior angle (in degrees)?

Answer key

  1. 24
  2. 73
  3. 38
  4. 15
  5. Yes
  6. 56
  7. Yes
  8. 8
  9. 79
  10. 98
  11. 100
  12. 61
  13. 100
  14. 20
  15. 8
  16. 24
  17. 90
  18. 37
  19. 36
  20. 11
  21. Yes
  22. 36
  23. 18
  24. 52
  25. 51
  26. 43
  27. 118
  28. 75
  29. 28
  30. 76
  31. 45
  32. 108
  33. 136
  34. 103
  35. 50
  36. 37
  37. No
  38. 103
  39. 48
  40. 135

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