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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 255 · 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.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 69°. What is the third angle (in degrees)?
  3. 3.In a right-angled triangle, one of the other two angles is 60°. What is the third angle (in degrees)?
  4. 4.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  5. 5.In triangle ABC, angle A = 55° and angle B = 100°. What is angle C (in degrees)?
  6. 6.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  7. 7.The two shorter sides of a right-angled triangle are 36 cm and 15 cm. How long is the longest side (in cm)?
  8. 8.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)?
  9. 9.In triangle ABC, angle A = 39° and angle B = 76°. What is angle C (in degrees)?
  10. 10.An exterior angle of a triangle is 95°. One of its two interior opposite angles is 48°. What is the other one (in degrees)?
  11. 11.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 64°. What is the third angle (in degrees)?
  13. 13.The two shorter sides of a right-angled triangle are 16 cm and 12 cm. How long is the longest side (in cm)?
  14. 14.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  15. 15.In triangle ABC, angle A = 20° and angle B = 83°. What is angle C (in degrees)?
  16. 16.The two shorter sides of a right-angled triangle are 12 cm and 9 cm. How long is the longest side (in cm)?
  17. 17.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  18. 18.An exterior angle of a triangle is 58°. One of its two interior opposite angles is 25°. What is the other one (in degrees)?
  19. 19.An exterior angle of a triangle is 80°. One of its two interior opposite angles is 51°. What is the other one (in degrees)?
  20. 20.In an isosceles triangle, the angle between the two equal sides is 64°. What is each of the other two angles (in degrees)?
  21. 21.In triangle ABC, angle A = 67° and angle B = 44°. What is angle C (in degrees)?
  22. 22.An exterior angle of a triangle is 65°. One of its two interior opposite angles is 39°. What is the other one (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 61°. What is the third angle (in degrees)?
  24. 24.In a right-angled triangle, one of the other two angles is 65°. What is the third angle (in degrees)?
  25. 25.An exterior angle of a triangle is 95°. One of its two interior opposite angles is 68°. What is the other one (in degrees)?
  26. 26.In an isosceles triangle, the two equal angles are 35° each. What is the third angle (in degrees)?
  27. 27.In a right-angled triangle, one of the other two angles is 79°. What is the third angle (in degrees)?
  28. 28.The longest side of a right-angled triangle is 39 cm and one of the other sides is 36 cm. How long is the third side (in cm)?
  29. 29.In triangle ABC, angle A = 58° and angle B = 84°. What is angle C (in degrees)?
  30. 30.In triangle ABC, angle A = 84° and angle B = 72°. What is angle C (in degrees)?
  31. 31.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  32. 32.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  33. 33.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  34. 34.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)?
  35. 35.In triangle ABC, angle A = 36° and angle B = 66°. What is angle C (in degrees)?
  36. 36.In an isosceles triangle, the two equal angles are 26° each. What is the third angle (in degrees)?
  37. 37.Can a triangle have sides of 20 cm, 11 cm and 4 cm? (a) Yes (b) No
  38. 38.In an isosceles triangle, the two equal angles are 53° each. What is the third angle (in degrees)?
  39. 39.In an isosceles triangle, the two equal angles are 66° each. What is the third angle (in degrees)?
  40. 40.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?

Answer key

  1. 72
  2. 21
  3. 30
  4. 80
  5. 25
  6. 90
  7. 39
  8. 12
  9. 65
  10. 47
  11. 45
  12. 26
  13. 20
  14. 17
  15. 77
  16. 15
  17. 18
  18. 33
  19. 29
  20. 58
  21. 69
  22. 26
  23. 29
  24. 25
  25. 27
  26. 110
  27. 11
  28. 15
  29. 38
  30. 24
  31. 90
  32. 75
  33. 20
  34. 15
  35. 78
  36. 128
  37. No
  38. 74
  39. 48
  40. 120

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