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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 315 · 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.

NameDateTime takenScore ___ / 40
  1. 1.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  2. 2.In triangle ABC, angle A = 42° and angle B = 50°. What is angle C (in degrees)?
  3. 3.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  4. 4.In an isosceles triangle, the two equal angles are 73° each. What is the third angle (in degrees)?
  5. 5.In an isosceles triangle, the two equal angles are 71° each. What is the third angle (in degrees)?
  6. 6.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  7. 7.In an isosceles triangle, the two equal angles are 37° each. What is the third angle (in degrees)?
  8. 8.The two interior opposite angles of a triangle are 60° and 67°. What is the exterior angle (in degrees)?
  9. 9.Can a triangle have sides of 20 cm, 4 cm and 12 cm? (a) Yes (b) No
  10. 10.Can a triangle have sides of 2 cm, 12 cm and 13 cm? (a) No (b) Yes
  11. 11.In triangle ABC, angle A = 24° and angle B = 121°. What is angle C (in degrees)?
  12. 12.In triangle ABC, angle A = 63° and angle B = 36°. What is angle C (in degrees)?
  13. 13.In triangle ABC, angle A = 56° and angle B = 99°. What is angle C (in degrees)?
  14. 14.The two shorter sides of a right-angled triangle are 18 cm and 24 cm. How long is the longest side (in cm)?
  15. 15.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  16. 16.In a right-angled triangle, one of the other two angles is 62°. What is the third angle (in degrees)?
  17. 17.An exterior angle of a triangle is 65°. One of its two interior opposite angles is 20°. What is the other one (in degrees)?
  18. 18.In a right-angled triangle, one of the other two angles is 33°. What is the third angle (in degrees)?
  19. 19.Can a triangle have sides of 11 cm, 7 cm and 21 cm? (a) No (b) Yes
  20. 20.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  21. 21.An exterior angle of a triangle is 77°. One of its two interior opposite angles is 26°. What is the other one (in degrees)?
  22. 22.In an isosceles triangle, the angle between the two equal sides is 124°. What is each of the other two angles (in degrees)?
  23. 23.An exterior angle of a triangle is 122°. One of its two interior opposite angles is 71°. What is the other one (in degrees)?
  24. 24.In an isosceles triangle, the two equal angles are 49° each. What is the third angle (in degrees)?
  25. 25.An exterior angle of a triangle is 88°. One of its two interior opposite angles is 67°. What is the other one (in degrees)?
  26. 26.In an isosceles triangle, the angle between the two equal sides is 110°. What is each of the other two angles (in degrees)?
  27. 27.In a right-angled triangle, one of the other two angles is 29°. What is the third angle (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 67°. What is the third angle (in degrees)?
  29. 29.An exterior angle of a triangle is 111°. One of its two interior opposite angles is 77°. What is the other one (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  31. 31.In triangle ABC, angle A = 37° and angle B = 100°. What is angle C (in degrees)?
  32. 32.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  33. 33.The two shorter sides of a right-angled triangle are 12 cm and 9 cm. How long is the longest side (in cm)?
  34. 34.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  35. 35.Can a triangle have sides of 9 cm, 19 cm and 5 cm? (a) Yes (b) No
  36. 36.The two interior opposite angles of a triangle are 29° and 55°. What is the exterior angle (in degrees)?
  37. 37.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)?
  38. 38.An exterior angle of a triangle is 86°. One of its two interior opposite angles is 66°. What is the other one (in degrees)?
  39. 39.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 62° and 76°. What is the exterior angle (in degrees)?

Answer key

  1. 39
  2. 88
  3. 72
  4. 34
  5. 38
  6. 80
  7. 106
  8. 127
  9. No
  10. Yes
  11. 35
  12. 81
  13. 25
  14. 30
  15. 90
  16. 28
  17. 45
  18. 57
  19. No
  20. 50
  21. 51
  22. 28
  23. 51
  24. 82
  25. 21
  26. 35
  27. 61
  28. 23
  29. 34
  30. 62
  31. 43
  32. 90
  33. 15
  34. 45
  35. No
  36. 84
  37. 24
  38. 20
  39. 40
  40. 138

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