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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 696 · 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.The two interior opposite angles of a triangle are 78° and 39°. What is the exterior angle (in degrees)?
  2. 2.In triangle ABC, angle A = 31° and angle B = 81°. What is angle C (in degrees)?
  3. 3.In triangle ABC, angle A = 49° and angle B = 20°. What is angle C (in degrees)?
  4. 4.In an isosceles triangle, the angle between the two equal sides is 70°. What is each of the other two angles (in degrees)?
  5. 5.An exterior angle of a triangle is 135°. One of its two interior opposite angles is 71°. What is the other one (in degrees)?
  6. 6.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)?
  7. 7.In triangle ABC, angle A = 69° and angle B = 46°. What is angle C (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 86°. One of its two interior opposite angles is 64°. What is the other one (in degrees)?
  10. 10.In an isosceles triangle, the two equal angles are 61° each. What is the third angle (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 79°. What is the third angle (in degrees)?
  12. 12.The two shorter sides of a right-angled triangle are 24 cm and 10 cm. How long is the longest side (in cm)?
  13. 13.In an isosceles triangle, the angle between the two equal sides is 30°. What is each of the other two angles (in degrees)?
  14. 14.In an isosceles triangle, the two equal angles are 58° each. What is the third angle (in degrees)?
  15. 15.In triangle ABC, angle A = 78° and angle B = 48°. What is angle C (in degrees)?
  16. 16.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  17. 17.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  18. 18.Can a triangle have sides of 10 cm, 10 cm and 4 cm? (a) Yes (b) No
  19. 19.In an isosceles triangle, the angle between the two equal sides is 96°. What is each of the other two angles (in degrees)?
  20. 20.An exterior angle of a triangle is 62°. One of its two interior opposite angles is 28°. What is the other one (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  22. 22.An exterior angle of a triangle is 93°. One of its two interior opposite angles is 73°. What is the other one (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 17°. What is the third angle (in degrees)?
  24. 24.In an isosceles triangle, the two equal angles are 41° each. What is the third angle (in degrees)?
  25. 25.Can a triangle have sides of 4 cm, 6 cm and 6 cm? (a) Yes (b) No
  26. 26.An exterior angle of a triangle is 137°. One of its two interior opposite angles is 77°. What is the other one (in degrees)?
  27. 27.In an isosceles triangle, the angle between the two equal sides is 102°. What is each of the other two angles (in degrees)?
  28. 28.An exterior angle of a triangle is 72°. One of its two interior opposite angles is 52°. What is the other one (in degrees)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 126°. What is each of the other two angles (in degrees)?
  30. 30.In an isosceles triangle, the two equal angles are 68° each. What is the third angle (in degrees)?
  31. 31.In an isosceles triangle, the two equal angles are 42° each. What is the third angle (in degrees)?
  32. 32.In triangle ABC, angle A = 46° and angle B = 58°. What is angle C (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 32° and 49°. What is the exterior angle (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 75°. What is the third angle (in degrees)?
  35. 35.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)?
  36. 36.In an isosceles triangle, the two equal angles are 53° each. What is the third angle (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 33°. What is the third angle (in degrees)?
  38. 38.Can a triangle have sides of 10 cm, 10 cm and 12 cm? (a) No (b) Yes
  39. 39.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  40. 40.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?

Answer key

  1. 117
  2. 68
  3. 111
  4. 55
  5. 64
  6. 18
  7. 65
  8. 80
  9. 22
  10. 58
  11. 11
  12. 26
  13. 75
  14. 64
  15. 54
  16. 54
  17. 50
  18. Yes
  19. 42
  20. 34
  21. 35
  22. 20
  23. 73
  24. 98
  25. Yes
  26. 60
  27. 39
  28. 20
  29. 27
  30. 44
  31. 96
  32. 76
  33. 81
  34. 15
  35. 15
  36. 74
  37. 57
  38. Yes
  39. 17
  40. 65

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