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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 143 · 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.An exterior angle of a triangle is 136°. One of its two interior opposite angles is 76°. What is the other one (in degrees)?
  2. 2.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  3. 3.In an isosceles triangle, the two equal angles are 58° each. What is the third angle (in degrees)?
  4. 4.Can a triangle have sides of 4 cm, 9 cm and 7 cm? (a) No (b) Yes
  5. 5.The longest side of a right-angled triangle is 26 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  6. 6.Can a triangle have sides of 5 cm, 4 cm and 7 cm? (a) Yes (b) No
  7. 7.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  8. 8.Can a triangle have sides of 10 cm, 10 cm and 1 cm? (a) Yes (b) No
  9. 9.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  10. 10.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  11. 11.The longest side of a right-angled triangle is 13 cm and one of the other sides is 5 cm. How long is the third side (in cm)?
  12. 12.In triangle ABC, angle A = 90° and angle B = 45°. What is angle C (in degrees)?
  13. 13.An exterior angle of a triangle is 77°. One of its two interior opposite angles is 53°. What is the other one (in degrees)?
  14. 14.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  15. 15.An exterior angle of a triangle is 79°. One of its two interior opposite angles is 40°. What is the other one (in degrees)?
  16. 16.In triangle ABC, angle A = 29° and angle B = 33°. What is angle C (in degrees)?
  17. 17.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  18. 18.In an isosceles triangle, the angle between the two equal sides is 50°. What is each of the other two angles (in degrees)?
  19. 19.In triangle ABC, angle A = 44° and angle B = 34°. What is angle C (in degrees)?
  20. 20.Can a triangle have sides of 11 cm, 22 cm and 10 cm? (a) No (b) Yes
  21. 21.The two interior opposite angles of a triangle are 31° and 22°. What is the exterior angle (in degrees)?
  22. 22.In an isosceles triangle, the angle between the two equal sides is 54°. What is each of the other two angles (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  24. 24.Can a triangle have sides of 7 cm, 4 cm and 8 cm? (a) No (b) Yes
  25. 25.An exterior angle of a triangle is 85°. One of its two interior opposite angles is 26°. What is the other one (in degrees)?
  26. 26.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  27. 27.In a right-angled triangle, one of the other two angles is 48°. What is the third angle (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 40°. What is the third angle (in degrees)?
  29. 29.In triangle ABC, angle A = 48° and angle B = 101°. What is angle C (in degrees)?
  30. 30.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  31. 31.In a right-angled triangle, one of the other two angles is 64°. What is the third angle (in degrees)?
  32. 32.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  33. 33.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)?
  34. 34.In a right-angled triangle, one of the other two angles is 56°. What is the third angle (in degrees)?
  35. 35.The longest side of a right-angled triangle is 25 cm and one of the other sides is 20 cm. How long is the third side (in cm)?
  36. 36.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  37. 37.In an isosceles triangle, the angle between the two equal sides is 138°. What is each of the other two angles (in degrees)?
  38. 38.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 78° and 30°. What is the exterior angle (in degrees)?

Answer key

  1. 60
  2. 20
  3. 64
  4. Yes
  5. 10
  6. Yes
  7. 90
  8. Yes
  9. 45
  10. 90
  11. 12
  12. 45
  13. 24
  14. 17
  15. 39
  16. 118
  17. 54
  18. 65
  19. 102
  20. No
  21. 53
  22. 63
  23. 76
  24. Yes
  25. 59
  26. 50
  27. 42
  28. 50
  29. 31
  30. 25
  31. 26
  32. 72
  33. 24
  34. 34
  35. 15
  36. 40
  37. 21
  38. 90
  39. 65
  40. 108

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