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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 4 · 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 a right-angled triangle, one of the other two angles is 73°. What is the third angle (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 78°. What is the third angle (in degrees)?
  3. 3.In triangle ABC, angle A = 43° and angle B = 85°. What is angle C (in degrees)?
  4. 4.Can a triangle have sides of 12 cm, 10 cm and 7 cm? (a) No (b) Yes
  5. 5.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  6. 6.The two interior opposite angles of a triangle are 68° and 37°. What is the exterior angle (in degrees)?
  7. 7.An exterior angle of a triangle is 112°. One of its two interior opposite angles is 78°. What is the other one (in degrees)?
  8. 8.In triangle ABC, angle A = 55° and angle B = 77°. What is angle C (in degrees)?
  9. 9.In an isosceles triangle, the two equal angles are 47° each. What is the third angle (in degrees)?
  10. 10.In triangle ABC, angle A = 55° and angle B = 61°. What is angle C (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 39°. What is the third angle (in degrees)?
  12. 12.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  13. 13.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  14. 14.An exterior angle of a triangle is 86°. One of its two interior opposite angles is 26°. What is the other one (in degrees)?
  15. 15.In an isosceles triangle, the two equal angles are 60° each. What is the third angle (in degrees)?
  16. 16.In triangle ABC, angle A = 72° and angle B = 38°. What is angle C (in degrees)?
  17. 17.In triangle ABC, angle A = 73° and angle B = 42°. What is angle C (in degrees)?
  18. 18.The two interior opposite angles of a triangle are 67° and 30°. What is the exterior angle (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 59°. What is the third angle (in degrees)?
  20. 20.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  21. 21.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  22. 22.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  23. 23.In triangle ABC, angle A = 66° and angle B = 42°. What is angle C (in degrees)?
  24. 24.Can a triangle have sides of 11 cm, 9 cm and 22 cm? (a) Yes (b) No
  25. 25.In triangle ABC, angle A = 49° and angle B = 36°. What is angle C (in degrees)?
  26. 26.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  27. 27.In triangle ABC, angle A = 21° and angle B = 113°. What is angle C (in degrees)?
  28. 28.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest 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 50°. What is the third angle (in degrees)?
  31. 31.In an isosceles triangle, the two equal angles are 74° each. What is the third angle (in degrees)?
  32. 32.An exterior angle of a triangle is 142°. One of its two interior opposite angles is 75°. What is the other one (in degrees)?
  33. 33.In a right-angled triangle, one of the other two angles is 23°. What is the third angle (in degrees)?
  34. 34.Can a triangle have sides of 8 cm, 4 cm and 5 cm? (a) Yes (b) No
  35. 35.Can a triangle have sides of 11 cm, 6 cm and 12 cm? (a) No (b) Yes
  36. 36.In an isosceles triangle, the angle between the two equal sides is 136°. What is each of the other two angles (in degrees)?
  37. 37.In an isosceles triangle, the two equal angles are 34° each. What is the third angle (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 72°. What is the third angle (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 69° and 72°. What is the exterior angle (in degrees)?

Answer key

  1. 17
  2. 12
  3. 52
  4. Yes
  5. 25
  6. 105
  7. 34
  8. 48
  9. 86
  10. 64
  11. 51
  12. 20
  13. 45
  14. 60
  15. 60
  16. 70
  17. 65
  18. 97
  19. 31
  20. 25
  21. 70
  22. 120
  23. 72
  24. No
  25. 95
  26. 100
  27. 46
  28. 72
  29. 80
  30. 40
  31. 32
  32. 67
  33. 67
  34. Yes
  35. Yes
  36. 22
  37. 112
  38. 18
  39. 52
  40. 141

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