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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 792 · 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.

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  1. 1.In a right-angled triangle, one of the other two angles is 73°. What is the third angle (in degrees)?
  2. 2.In an isosceles triangle, the two equal angles are 40° each. What is the third angle (in degrees)?
  3. 3.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  4. 4.An exterior angle of a triangle is 65°. One of its two interior opposite angles is 33°. What is the other one (in degrees)?
  5. 5.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  6. 6.In a right-angled triangle, one of the other two angles is 37°. What is the third angle (in degrees)?
  7. 7.In an isosceles triangle, the two equal angles are 72° each. What is the third angle (in degrees)?
  8. 8.In triangle ABC, angle A = 51° and angle B = 82°. What is angle C (in degrees)?
  9. 9.In triangle ABC, angle A = 99° and angle B = 20°. What is angle C (in degrees)?
  10. 10.In an isosceles triangle, the angle between the two equal sides is 88°. What is each of the other two angles (in degrees)?
  11. 11.Can a triangle have sides of 10 cm, 6 cm and 9 cm? (a) No (b) Yes
  12. 12.The longest side of a right-angled triangle is 30 cm and one of the other sides is 18 cm. How long is the third side (in cm)?
  13. 13.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  14. 14.In an isosceles triangle, the two equal angles are 84° each. What is the third angle (in degrees)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 44°. What is each of the other two angles (in degrees)?
  16. 16.In triangle ABC, angle A = 100° and angle B = 25°. What is angle C (in degrees)?
  17. 17.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  18. 18.In triangle ABC, angle A = 92° and angle B = 48°. What is angle C (in degrees)?
  19. 19.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 65°. What is the third angle (in degrees)?
  21. 21.In an isosceles triangle, the angle between the two equal sides is 124°. What is each of the other two angles (in degrees)?
  22. 22.In triangle ABC, angle A = 52° and angle B = 40°. What is angle C (in degrees)?
  23. 23.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)?
  24. 24.In a right-angled triangle, one of the other two angles is 43°. What is the third angle (in degrees)?
  25. 25.The two interior opposite angles of a triangle are 45° and 43°. What is the exterior angle (in degrees)?
  26. 26.In triangle ABC, angle A = 32° and angle B = 49°. What is angle C (in degrees)?
  27. 27.The two interior opposite angles of a triangle are 80° and 58°. What is the exterior angle (in degrees)?
  28. 28.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  29. 29.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 30°. What is the third angle (in degrees)?
  31. 31.In triangle ABC, angle A = 83° and angle B = 20°. What is angle C (in degrees)?
  32. 32.The two interior opposite angles of a triangle are 69° and 74°. What is the exterior angle (in degrees)?
  33. 33.Can a triangle have sides of 4 cm, 3 cm and 2 cm? (a) No (b) Yes
  34. 34.Can a triangle have sides of 21 cm, 12 cm and 9 cm? (a) No (b) Yes
  35. 35.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  36. 36.Can a triangle have sides of 6 cm, 3 cm and 2 cm? (a) No (b) Yes
  37. 37.In a right-angled triangle, one of the other two angles is 46°. What is the third angle (in degrees)?
  38. 38.An exterior angle of a triangle is 69°. One of its two interior opposite angles is 20°. What is the other one (in degrees)?
  39. 39.In triangle ABC, angle A = 34° and angle B = 48°. What is angle C (in degrees)?
  40. 40.In an isosceles triangle, the angle between the two equal sides is 104°. What is each of the other two angles (in degrees)?

Answer key

  1. 17
  2. 100
  3. 45
  4. 32
  5. 100
  6. 53
  7. 36
  8. 47
  9. 61
  10. 46
  11. Yes
  12. 24
  13. 20
  14. 12
  15. 68
  16. 55
  17. 90
  18. 40
  19. 100
  20. 25
  21. 28
  22. 88
  23. 24
  24. 47
  25. 88
  26. 99
  27. 138
  28. 54
  29. 80
  30. 60
  31. 77
  32. 143
  33. Yes
  34. No
  35. 39
  36. No
  37. 44
  38. 49
  39. 98
  40. 38

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