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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 306 · 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.

NameDateTime takenScore ___ / 40
  1. 1.Can a triangle have sides of 9 cm, 19 cm and 10 cm? (a) Yes (b) No
  2. 2.The two interior opposite angles of a triangle are 71° and 29°. What is the exterior angle (in degrees)?
  3. 3.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)?
  4. 4.In an isosceles triangle, the two equal angles are 45° each. What is the third angle (in degrees)?
  5. 5.In triangle ABC, angle A = 36° and angle B = 67°. What is angle C (in degrees)?
  6. 6.An exterior angle of a triangle is 137°. One of its two interior opposite angles is 64°. What is the other one (in degrees)?
  7. 7.Can a triangle have sides of 5 cm, 10 cm and 13 cm? (a) No (b) Yes
  8. 8.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  9. 9.The two interior opposite angles of a triangle are 20° and 44°. What is the exterior angle (in degrees)?
  10. 10.The two interior opposite angles of a triangle are 39° and 39°. What is the exterior angle (in degrees)?
  11. 11.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)?
  12. 12.In triangle ABC, angle A = 40° and angle B = 102°. What is angle C (in degrees)?
  13. 13.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)?
  14. 14.In a right-angled triangle, one of the other two angles is 74°. What is the third angle (in degrees)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 80°. What is each of the other two angles (in degrees)?
  16. 16.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  17. 17.Can a triangle have sides of 7 cm, 7 cm and 16 cm? (a) Yes (b) No
  18. 18.In a right-angled triangle, one of the other two angles is 31°. What is the third angle (in degrees)?
  19. 19.Can a triangle have sides of 6 cm, 12 cm and 10 cm? (a) No (b) Yes
  20. 20.An exterior angle of a triangle is 116°. One of its two interior opposite angles is 67°. What is the other one (in degrees)?
  21. 21.An exterior angle of a triangle is 130°. One of its two interior opposite angles is 73°. What is the other one (in degrees)?
  22. 22.In an isosceles triangle, the angle between the two equal sides is 138°. What is each of the other two angles (in degrees)?
  23. 23.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  24. 24.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  25. 25.Can a triangle have sides of 3 cm, 8 cm and 3 cm? (a) Yes (b) No
  26. 26.The two shorter sides of a right-angled triangle are 24 cm and 10 cm. How long is the longest side (in cm)?
  27. 27.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)?
  28. 28.An exterior angle of a triangle is 70°. One of its two interior opposite angles is 22°. What is the other one (in degrees)?
  29. 29.An exterior angle of a triangle is 106°. One of its two interior opposite angles is 26°. What is the other one (in degrees)?
  30. 30.In an isosceles triangle, the two equal angles are 85° each. What is the third angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  32. 32.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)?
  33. 33.In an isosceles triangle, the two equal angles are 55° each. What is the third angle (in degrees)?
  34. 34.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 44°. What is the third angle (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 22°. What is the third angle (in degrees)?
  37. 37.The two interior opposite angles of a triangle are 26° and 36°. What is the exterior angle (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  39. 39.In triangle ABC, angle A = 53° and angle B = 42°. What is angle C (in degrees)?
  40. 40.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?

Answer key

  1. No
  2. 100
  3. 5
  4. 90
  5. 77
  6. 73
  7. Yes
  8. 90
  9. 64
  10. 78
  11. 20
  12. 38
  13. 24
  14. 16
  15. 50
  16. 20
  17. No
  18. 59
  19. Yes
  20. 49
  21. 57
  22. 21
  23. 84
  24. 36
  25. No
  26. 26
  27. 15
  28. 48
  29. 80
  30. 10
  31. 62
  32. 12
  33. 70
  34. 20
  35. 46
  36. 68
  37. 62
  38. 79
  39. 85
  40. 17

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