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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 795 · 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 an isosceles triangle, the two equal angles are 59° each. What is the third angle (in degrees)?
  2. 2.In triangle ABC, angle A = 21° and angle B = 110°. What is angle C (in degrees)?
  3. 3.In a right-angled triangle, one of the other two angles is 47°. What is the third angle (in degrees)?
  4. 4.In triangle ABC, angle A = 24° and angle B = 112°. What is angle C (in degrees)?
  5. 5.In triangle ABC, angle A = 91° and angle B = 44°. What is angle C (in degrees)?
  6. 6.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  7. 7.Can a triangle have sides of 11 cm, 5 cm and 10 cm? (a) Yes (b) No
  8. 8.In triangle ABC, angle A = 95° and angle B = 34°. What is angle C (in degrees)?
  9. 9.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)?
  10. 10.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  11. 11.The two interior opposite angles of a triangle are 74° and 57°. What is the exterior angle (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 35°. What is the third angle (in degrees)?
  13. 13.In triangle ABC, angle A = 82° and angle B = 39°. What is angle C (in degrees)?
  14. 14.The two interior opposite angles of a triangle are 57° and 20°. What is the exterior angle (in degrees)?
  15. 15.An exterior angle of a triangle is 123°. One of its two interior opposite angles is 70°. What is the other one (in degrees)?
  16. 16.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  17. 17.In an isosceles triangle, the angle between the two equal sides is 98°. What is each of the other two angles (in degrees)?
  18. 18.The two interior opposite angles of a triangle are 38° and 72°. What is the exterior angle (in degrees)?
  19. 19.In an isosceles triangle, the two equal angles are 69° each. What is the third angle (in degrees)?
  20. 20.In triangle ABC, angle A = 32° and angle B = 20°. What is angle C (in degrees)?
  21. 21.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  22. 22.An exterior angle of a triangle is 67°. One of its two interior opposite angles is 20°. What is the other one (in degrees)?
  23. 23.In an isosceles triangle, the two equal angles are 25° each. What is the third angle (in degrees)?
  24. 24.Can a triangle have sides of 9 cm, 11 cm and 4 cm? (a) No (b) Yes
  25. 25.In triangle ABC, angle A = 73° and angle B = 29°. What is angle C (in degrees)?
  26. 26.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)?
  27. 27.The two interior opposite angles of a triangle are 23° and 22°. What is the exterior angle (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 32°. What is the third angle (in degrees)?
  29. 29.The two shorter sides of a right-angled triangle are 12 cm and 5 cm. How long is the longest side (in cm)?
  30. 30.The longest side of a right-angled triangle is 20 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  31. 31.In an isosceles triangle, the angle between the two equal sides is 60°. What is each of the other two angles (in degrees)?
  32. 32.In an isosceles triangle, the angle between the two equal sides is 124°. What is each of the other two angles (in degrees)?
  33. 33.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  34. 34.In triangle ABC, angle A = 74° and angle B = 55°. What is angle C (in degrees)?
  35. 35.Can a triangle have sides of 8 cm, 7 cm and 9 cm? (a) Yes (b) No
  36. 36.Can a triangle have sides of 9 cm, 21 cm and 9 cm? (a) No (b) Yes
  37. 37.Can a triangle have sides of 8 cm, 7 cm and 16 cm? (a) Yes (b) No
  38. 38.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)?
  39. 39.In an isosceles triangle, the two equal angles are 44° each. What is the third angle (in degrees)?
  40. 40.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?

Answer key

  1. 62
  2. 49
  3. 43
  4. 44
  5. 45
  6. 20
  7. Yes
  8. 51
  9. 15
  10. 17
  11. 131
  12. 55
  13. 59
  14. 77
  15. 53
  16. 50
  17. 41
  18. 110
  19. 42
  20. 128
  21. 36
  22. 47
  23. 130
  24. Yes
  25. 78
  26. 7
  27. 45
  28. 58
  29. 13
  30. 16
  31. 60
  32. 28
  33. 65
  34. 51
  35. Yes
  36. No
  37. No
  38. 24
  39. 92
  40. 100

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