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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 435 · 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 an isosceles triangle, the angle between the two equal sides is 146°. What is each of the other two angles (in degrees)?
  2. 2.In an isosceles triangle, the angle between the two equal sides is 102°. What is each of the other two angles (in degrees)?
  3. 3.In a right-angled triangle, one of the other two angles is 79°. What is the third angle (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  5. 5.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  6. 6.The longest side of a right-angled triangle is 15 cm and one of the other sides is 9 cm. How long is the third side (in cm)?
  7. 7.An exterior angle of a triangle is 58°. One of its two interior opposite angles is 28°. What is the other one (in degrees)?
  8. 8.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  9. 9.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  10. 10.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  11. 11.In an isosceles triangle, the two equal angles are 83° each. What is the third angle (in degrees)?
  12. 12.In triangle ABC, angle A = 28° and angle B = 22°. What is angle C (in degrees)?
  13. 13.In an isosceles triangle, the two equal angles are 42° each. What is the third angle (in degrees)?
  14. 14.The two shorter sides of a right-angled triangle are 20 cm and 15 cm. How long is the longest side (in cm)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 42°. What is each of the other two angles (in degrees)?
  16. 16.The two interior opposite angles of a triangle are 74° and 74°. What is the exterior angle (in degrees)?
  17. 17.Can a triangle have sides of 5 cm, 10 cm and 9 cm? (a) No (b) Yes
  18. 18.The two interior opposite angles of a triangle are 63° and 28°. What is the exterior angle (in degrees)?
  19. 19.In triangle ABC, angle A = 41° and angle B = 34°. What is angle C (in degrees)?
  20. 20.An exterior angle of a triangle is 116°. One of its two interior opposite angles is 68°. What is the other one (in degrees)?
  21. 21.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)?
  22. 22.In an isosceles triangle, the two equal angles are 38° each. What is the third angle (in degrees)?
  23. 23.In triangle ABC, angle A = 69° and angle B = 29°. What is angle C (in degrees)?
  24. 24.In a right-angled triangle, one of the other two angles is 46°. What is the third angle (in degrees)?
  25. 25.In triangle ABC, angle A = 47° and angle B = 47°. What is angle C (in degrees)?
  26. 26.In triangle ABC, angle A = 100° and angle B = 35°. What is angle C (in degrees)?
  27. 27.An exterior angle of a triangle is 105°. One of its two interior opposite angles is 70°. What is the other one (in degrees)?
  28. 28.In triangle ABC, angle A = 44° and angle B = 50°. What is angle C (in degrees)?
  29. 29.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  31. 31.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  32. 32.In triangle ABC, angle A = 78° and angle B = 51°. What is angle C (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 39° and 31°. What is the exterior angle (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 42°. What is the third angle (in degrees)?
  35. 35.Can a triangle have sides of 3 cm, 10 cm and 10 cm? (a) Yes (b) No
  36. 36.In triangle ABC, angle A = 86° and angle B = 70°. What is angle C (in degrees)?
  37. 37.In an isosceles triangle, the two equal angles are 24° each. What is the third angle (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 19°. What is the third angle (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 18°. What is the third angle (in degrees)?
  40. 40.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?

Answer key

  1. 17
  2. 39
  3. 11
  4. 80
  5. 36
  6. 12
  7. 30
  8. 25
  9. 36
  10. 90
  11. 14
  12. 130
  13. 96
  14. 25
  15. 69
  16. 148
  17. Yes
  18. 91
  19. 105
  20. 48
  21. 7
  22. 104
  23. 82
  24. 44
  25. 86
  26. 45
  27. 35
  28. 86
  29. 90
  30. 74
  31. 20
  32. 51
  33. 70
  34. 48
  35. Yes
  36. 24
  37. 132
  38. 71
  39. 72
  40. 90

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