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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 210 · 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.Can a triangle have sides of 9 cm, 8 cm and 10 cm? (a) Yes (b) No
  2. 2.An exterior angle of a triangle is 65°. One of its two interior opposite angles is 43°. What is the other one (in degrees)?
  3. 3.In triangle ABC, angle A = 33° and angle B = 38°. What is angle C (in degrees)?
  4. 4.An exterior angle of a triangle is 130°. One of its two interior opposite angles is 51°. What is the other one (in degrees)?
  5. 5.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  6. 6.In an isosceles triangle, the two equal angles are 28° each. What is the third angle (in degrees)?
  7. 7.The longest side of a right-angled triangle is 15 cm and one of the other sides is 9 cm. How long is the third side (in cm)?
  8. 8.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  9. 9.The longest side of a right-angled triangle is 5 cm and one of the other sides is 3 cm. How long is the third side (in cm)?
  10. 10.In a right-angled triangle, one of the other two angles is 54°. What is the third angle (in degrees)?
  11. 11.The longest side of a right-angled triangle is 30 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  12. 12.In an isosceles triangle, the two equal angles are 63° each. What is the third angle (in degrees)?
  13. 13.The two interior opposite angles of a triangle are 80° and 47°. What is the exterior angle (in degrees)?
  14. 14.In triangle ABC, angle A = 99° and angle B = 47°. What is angle C (in degrees)?
  15. 15.The longest side of a right-angled triangle is 20 cm and one of the other sides is 16 cm. How long is the third side (in cm)?
  16. 16.In triangle ABC, angle A = 44° and angle B = 30°. What is angle C (in degrees)?
  17. 17.An exterior angle of a triangle is 83°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?
  18. 18.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 64°. What is the third angle (in degrees)?
  20. 20.In triangle ABC, angle A = 25° and angle B = 25°. What is angle C (in degrees)?
  21. 21.In triangle ABC, angle A = 77° and angle B = 65°. What is angle C (in degrees)?
  22. 22.In a right-angled triangle, one of the other two angles is 44°. What is the third angle (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 23°. What is the third angle (in degrees)?
  24. 24.Can a triangle have sides of 5 cm, 8 cm and 6 cm? (a) Yes (b) No
  25. 25.An exterior angle of a triangle is 155°. One of its two interior opposite angles is 79°. What is the other one (in degrees)?
  26. 26.The two interior opposite angles of a triangle are 42° and 57°. What is the exterior angle (in degrees)?
  27. 27.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  28. 28.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)?
  29. 29.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  30. 30.In triangle ABC, angle A = 68° and angle B = 38°. What is angle C (in degrees)?
  31. 31.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  32. 32.Can a triangle have sides of 3 cm, 4 cm and 2 cm? (a) No (b) Yes
  33. 33.The two shorter sides of a right-angled triangle are 18 cm and 24 cm. How long is the longest side (in cm)?
  34. 34.The longest side of a right-angled triangle is 25 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  35. 35.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  37. 37.The two interior opposite angles of a triangle are 22° and 29°. What is the exterior angle (in degrees)?
  38. 38.The two interior opposite angles of a triangle are 33° and 46°. What is the exterior angle (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 36°. What is the third angle (in degrees)?
  40. 40.In triangle ABC, angle A = 96° and angle B = 47°. What is angle C (in degrees)?

Answer key

  1. Yes
  2. 22
  3. 109
  4. 79
  5. 40
  6. 124
  7. 12
  8. 25
  9. 4
  10. 36
  11. 18
  12. 54
  13. 127
  14. 34
  15. 12
  16. 106
  17. 53
  18. 36
  19. 26
  20. 130
  21. 38
  22. 46
  23. 67
  24. Yes
  25. 76
  26. 99
  27. 72
  28. 15
  29. 36
  30. 74
  31. 90
  32. Yes
  33. 30
  34. 7
  35. 65
  36. 80
  37. 51
  38. 79
  39. 54
  40. 37

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