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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 325 · 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 longest side of a right-angled triangle is 17 cm and one of the other sides is 8 cm. How long is the third side (in cm)?
  2. 2.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  3. 3.The two interior opposite angles of a triangle are 58° and 42°. What is the exterior angle (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 58°. What is the third angle (in degrees)?
  5. 5.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  6. 6.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  7. 7.In a right-angled triangle, one of the other two angles is 41°. What is the third angle (in degrees)?
  8. 8.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  9. 9.An exterior angle of a triangle is 111°. One of its two interior opposite angles is 33°. What is the other one (in degrees)?
  10. 10.The two interior opposite angles of a triangle are 80° and 20°. What is the exterior angle (in degrees)?
  11. 11.In triangle ABC, angle A = 64° and angle B = 49°. What is angle C (in degrees)?
  12. 12.In an isosceles triangle, the two equal angles are 56° each. What is the third angle (in degrees)?
  13. 13.In an isosceles triangle, the two equal angles are 68° each. What is the third angle (in degrees)?
  14. 14.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  15. 15.In triangle ABC, angle A = 53° and angle B = 94°. What is angle C (in degrees)?
  16. 16.In a right-angled triangle, one of the other two angles is 44°. What is the third angle (in degrees)?
  17. 17.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  18. 18.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 74°. What is the third angle (in degrees)?
  20. 20.The two interior opposite angles of a triangle are 25° and 56°. What is the exterior angle (in degrees)?
  21. 21.In triangle ABC, angle A = 38° and angle B = 36°. What is angle C (in degrees)?
  22. 22.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  23. 23.In an isosceles triangle, the two equal angles are 54° each. What is the third angle (in degrees)?
  24. 24.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  25. 25.In triangle ABC, angle A = 56° and angle B = 30°. What is angle C (in degrees)?
  26. 26.In triangle ABC, angle A = 45° and angle B = 39°. What is angle C (in degrees)?
  27. 27.In a right-angled triangle, one of the other two angles is 59°. What is the third angle (in degrees)?
  28. 28.The longest side of a right-angled triangle is 13 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  29. 29.In triangle ABC, angle A = 34° and angle B = 75°. What is angle C (in degrees)?
  30. 30.In an isosceles triangle, the two equal angles are 34° each. What is the third angle (in degrees)?
  31. 31.In triangle ABC, angle A = 66° and angle B = 57°. What is angle C (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 40°. What is the third angle (in degrees)?
  33. 33.The longest side of a right-angled triangle is 39 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  34. 34.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  35. 35.In triangle ABC, angle A = 87° and angle B = 67°. What is angle C (in degrees)?
  36. 36.In triangle ABC, angle A = 68° and angle B = 72°. What is angle C (in degrees)?
  37. 37.Can a triangle have sides of 8 cm, 24 cm and 11 cm? (a) Yes (b) No
  38. 38.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  39. 39.An exterior angle of a triangle is 117°. One of its two interior opposite angles is 78°. What is the other one (in degrees)?
  40. 40.In a right-angled triangle, one of the other two angles is 43°. What is the third angle (in degrees)?

Answer key

  1. 15
  2. 90
  3. 100
  4. 32
  5. 70
  6. 100
  7. 49
  8. 80
  9. 78
  10. 100
  11. 67
  12. 68
  13. 44
  14. 90
  15. 33
  16. 46
  17. 17
  18. 90
  19. 16
  20. 81
  21. 106
  22. 45
  23. 72
  24. 25
  25. 94
  26. 96
  27. 31
  28. 5
  29. 71
  30. 112
  31. 57
  32. 50
  33. 36
  34. 17
  35. 26
  36. 40
  37. No
  38. 54
  39. 39
  40. 47

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