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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 821 · 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.In triangle ABC, angle A = 94° and angle B = 31°. What is angle C (in degrees)?
  2. 2.An exterior angle of a triangle is 135°. One of its two interior opposite angles is 70°. What is the other one (in degrees)?
  3. 3.In triangle ABC, angle A = 34° and angle B = 68°. What is angle C (in degrees)?
  4. 4.In triangle ABC, angle A = 90° and angle B = 35°. What is angle C (in degrees)?
  5. 5.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)?
  6. 6.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  7. 7.The two interior opposite angles of a triangle are 41° and 22°. What is the exterior angle (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 15°. What is the third angle (in degrees)?
  9. 9.The two interior opposite angles of a triangle are 30° and 54°. What is the exterior angle (in degrees)?
  10. 10.In triangle ABC, angle A = 51° and angle B = 86°. What is angle C (in degrees)?
  11. 11.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)?
  12. 12.In an isosceles triangle, the angle between the two equal sides is 110°. What is each of the other two angles (in degrees)?
  13. 13.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)?
  14. 14.In triangle ABC, angle A = 40° and angle B = 26°. What is angle C (in degrees)?
  15. 15.Can a triangle have sides of 17 cm, 8 cm and 10 cm? (a) Yes (b) No
  16. 16.In triangle ABC, angle A = 36° and angle B = 99°. What is angle C (in degrees)?
  17. 17.In an isosceles triangle, the two equal angles are 35° each. What is the third angle (in degrees)?
  18. 18.In a right-angled triangle, one of the other two angles is 78°. What is the third angle (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  20. 20.An exterior angle of a triangle is 128°. One of its two interior opposite angles is 76°. What is the other one (in degrees)?
  21. 21.Can a triangle have sides of 18 cm, 7 cm and 7 cm? (a) No (b) Yes
  22. 22.In a right-angled triangle, one of the other two angles is 60°. What is the third angle (in degrees)?
  23. 23.Can a triangle have sides of 7 cm, 15 cm and 5 cm? (a) Yes (b) No
  24. 24.In an isosceles triangle, the two equal angles are 24° each. What is the third angle (in degrees)?
  25. 25.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)?
  26. 26.The two interior opposite angles of a triangle are 42° and 78°. What is the exterior angle (in degrees)?
  27. 27.In triangle ABC, angle A = 31° and angle B = 89°. What is angle C (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 50°. What is the third angle (in degrees)?
  29. 29.An exterior angle of a triangle is 86°. One of its two interior opposite angles is 64°. What is the other one (in degrees)?
  30. 30.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)?
  31. 31.In an isosceles triangle, the two equal angles are 73° each. What is the third angle (in degrees)?
  32. 32.In triangle ABC, angle A = 65° and angle B = 71°. What is angle C (in degrees)?
  33. 33.In a right-angled triangle, one of the other two angles is 49°. What is the third angle (in degrees)?
  34. 34.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 31°. What is the third angle (in degrees)?
  36. 36.In triangle ABC, angle A = 28° and angle B = 28°. What is angle C (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 67°. What is the third angle (in degrees)?
  38. 38.In an isosceles triangle, the two equal angles are 51° each. What is the third angle (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 44°. What is the third angle (in degrees)?
  40. 40.An exterior angle of a triangle is 116°. One of its two interior opposite angles is 76°. What is the other one (in degrees)?

Answer key

  1. 55
  2. 65
  3. 78
  4. 55
  5. 12
  6. 20
  7. 63
  8. 75
  9. 84
  10. 43
  11. 24
  12. 35
  13. 7
  14. 114
  15. Yes
  16. 45
  17. 110
  18. 12
  19. 22
  20. 52
  21. No
  22. 30
  23. No
  24. 132
  25. 12
  26. 120
  27. 60
  28. 40
  29. 22
  30. 15
  31. 34
  32. 44
  33. 41
  34. 36
  35. 59
  36. 124
  37. 23
  38. 78
  39. 46
  40. 40

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