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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 79 · 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.An exterior angle of a triangle is 69°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?
  2. 2.In an isosceles triangle, the angle between the two equal sides is 78°. What is each of the other two angles (in degrees)?
  3. 3.The two interior opposite angles of a triangle are 69° and 20°. What is the exterior angle (in degrees)?
  4. 4.In an isosceles triangle, the two equal angles are 74° each. What is the third angle (in degrees)?
  5. 5.In triangle ABC, angle A = 25° and angle B = 21°. What is angle C (in degrees)?
  6. 6.In an isosceles triangle, the angle between the two equal sides is 54°. What is each of the other two angles (in degrees)?
  7. 7.In an isosceles triangle, the angle between the two equal sides is 48°. What is each of the other two angles (in degrees)?
  8. 8.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)?
  9. 9.The two shorter sides of a right-angled triangle are 12 cm and 9 cm. How long is the longest side (in cm)?
  10. 10.In a right-angled triangle, one of the other two angles is 79°. What is the third angle (in degrees)?
  11. 11.In an isosceles triangle, the two equal angles are 61° each. What is the third angle (in degrees)?
  12. 12.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  13. 13.In triangle ABC, angle A = 72° and angle B = 60°. What is angle C (in degrees)?
  14. 14.The longest side of a right-angled triangle is 25 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  15. 15.Can a triangle have sides of 22 cm, 11 cm and 10 cm? (a) No (b) Yes
  16. 16.The longest side of a right-angled triangle is 39 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  17. 17.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  18. 18.In triangle ABC, angle A = 32° and angle B = 93°. What is angle C (in degrees)?
  19. 19.In triangle ABC, angle A = 27° and angle B = 91°. What is angle C (in degrees)?
  20. 20.Can a triangle have sides of 9 cm, 18 cm and 12 cm? (a) Yes (b) No
  21. 21.Can a triangle have sides of 9 cm, 9 cm and 22 cm? (a) Yes (b) No
  22. 22.An exterior angle of a triangle is 132°. One of its two interior opposite angles is 59°. What is the other one (in degrees)?
  23. 23.The two interior opposite angles of a triangle are 35° and 53°. What is the exterior angle (in degrees)?
  24. 24.In a right-angled triangle, one of the other two angles is 37°. What is the third angle (in degrees)?
  25. 25.In a right-angled triangle, one of the other two angles is 54°. What is the third angle (in degrees)?
  26. 26.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  27. 27.Can a triangle have sides of 9 cm, 9 cm and 19 cm? (a) Yes (b) No
  28. 28.Can a triangle have sides of 13 cm, 4 cm and 5 cm? (a) No (b) Yes
  29. 29.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  30. 30.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  31. 31.The two interior opposite angles of a triangle are 33° and 25°. What is the exterior angle (in degrees)?
  32. 32.In an isosceles triangle, the angle between the two equal sides is 56°. What is each of the other two angles (in degrees)?
  33. 33.Can a triangle have sides of 15 cm, 5 cm and 5 cm? (a) Yes (b) No
  34. 34.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  35. 35.In triangle ABC, angle A = 23° and angle B = 115°. What is angle C (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 26°. What is the third angle (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 65°. What is the third angle (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  39. 39.Can a triangle have sides of 10 cm, 17 cm and 7 cm? (a) No (b) Yes
  40. 40.An exterior angle of a triangle is 60°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?

Answer key

  1. 39
  2. 51
  3. 89
  4. 32
  5. 134
  6. 63
  7. 66
  8. 16
  9. 15
  10. 11
  11. 58
  12. 72
  13. 48
  14. 20
  15. No
  16. 36
  17. 17
  18. 55
  19. 62
  20. Yes
  21. No
  22. 73
  23. 88
  24. 53
  25. 36
  26. 22
  27. No
  28. No
  29. 70
  30. 45
  31. 58
  32. 62
  33. No
  34. 35
  35. 42
  36. 64
  37. 25
  38. 74
  39. No
  40. 30

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