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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 251 · 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 : 4 : 5. What is the smallest angle (in degrees)?
  2. 2.In triangle ABC, angle A = 20° and angle B = 56°. What is angle C (in degrees)?
  3. 3.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  4. 4.An exterior angle of a triangle is 146°. One of its two interior opposite angles is 69°. What is the other one (in degrees)?
  5. 5.The longest side of a right-angled triangle is 13 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  6. 6.In a right-angled triangle, one of the other two angles is 69°. What is the third angle (in degrees)?
  7. 7.Can a triangle have sides of 16 cm, 5 cm and 7 cm? (a) No (b) Yes
  8. 8.The two shorter sides of a right-angled triangle are 5 cm and 12 cm. How long is the longest side (in cm)?
  9. 9.In triangle ABC, angle A = 96° and angle B = 56°. What is angle C (in degrees)?
  10. 10.Can a triangle have sides of 5 cm, 13 cm and 3 cm? (a) Yes (b) No
  11. 11.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  12. 12.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  13. 13.The two interior opposite angles of a triangle are 76° and 42°. What is the exterior angle (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 76°. What is the third angle (in degrees)?
  16. 16.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  17. 17.In triangle ABC, angle A = 54° and angle B = 51°. What is angle C (in degrees)?
  18. 18.In an isosceles triangle, the angle between the two equal sides is 144°. What is each of the other two angles (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 67°. What is the third angle (in degrees)?
  20. 20.In an isosceles triangle, the angle between the two equal sides is 36°. What is each of the other two angles (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 70°. What is the third angle (in degrees)?
  22. 22.In an isosceles triangle, the angle between the two equal sides is 88°. What is each of the other two angles (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  24. 24.The longest side of a right-angled triangle is 26 cm and one of the other sides is 10 cm. How long is the third side (in cm)?
  25. 25.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  26. 26.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  27. 27.In an isosceles triangle, the two equal angles are 59° each. What is the third angle (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  29. 29.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  30. 30.In an isosceles triangle, the two equal angles are 23° each. What is the third angle (in degrees)?
  31. 31.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 50°. What is the third angle (in degrees)?
  33. 33.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)?
  34. 34.Can a triangle have sides of 6 cm, 7 cm and 2 cm? (a) Yes (b) No
  35. 35.In an isosceles triangle, the angle between the two equal sides is 100°. What is each of the other two angles (in degrees)?
  36. 36.Can a triangle have sides of 6 cm, 3 cm and 4 cm? (a) No (b) Yes
  37. 37.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  38. 38.The longest side of a right-angled triangle is 30 cm and one of the other sides is 18 cm. How long is the third side (in cm)?
  39. 39.An exterior angle of a triangle is 83°. One of its two interior opposite angles is 50°. What is the other one (in degrees)?
  40. 40.Can a triangle have sides of 16 cm, 6 cm and 6 cm? (a) No (b) Yes

Answer key

  1. 45
  2. 104
  3. 36
  4. 77
  5. 5
  6. 21
  7. No
  8. 13
  9. 28
  10. No
  11. 17
  12. 17
  13. 118
  14. 62
  15. 14
  16. 20
  17. 75
  18. 18
  19. 23
  20. 72
  21. 20
  22. 46
  23. 79
  24. 24
  25. 20
  26. 70
  27. 62
  28. 74
  29. 65
  30. 134
  31. 75
  32. 40
  33. 15
  34. Yes
  35. 40
  36. Yes
  37. 70
  38. 24
  39. 33
  40. No

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