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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 177 · 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 a right-angled triangle, one of the other two angles is 60°. What is the third angle (in degrees)?
  2. 2.In triangle ABC, angle A = 84° and angle B = 73°. What is angle C (in degrees)?
  3. 3.The longest side of a right-angled triangle is 30 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  4. 4.The two interior opposite angles of a triangle are 52° and 80°. What is the exterior angle (in degrees)?
  5. 5.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  6. 6.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)?
  7. 7.In a right-angled triangle, one of the other two angles is 35°. What is the third angle (in degrees)?
  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 an isosceles triangle, the angle between the two equal sides is 36°. What is each of the other two angles (in degrees)?
  10. 10.An exterior angle of a triangle is 105°. One of its two interior opposite angles is 70°. What is the other one (in degrees)?
  11. 11.In triangle ABC, angle A = 64° and angle B = 70°. What is angle C (in degrees)?
  12. 12.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  13. 13.In an isosceles triangle, the angle between the two equal sides is 142°. What is each of the other two angles (in degrees)?
  14. 14.In triangle ABC, angle A = 68° and angle B = 59°. What is angle C (in degrees)?
  15. 15.In an isosceles triangle, the two equal angles are 20° each. What is the third angle (in degrees)?
  16. 16.In a right-angled triangle, one of the other two angles is 45°. What is the third angle (in degrees)?
  17. 17.In a right-angled triangle, one of the other two angles is 71°. What is the third angle (in degrees)?
  18. 18.Can a triangle have sides of 14 cm, 8 cm and 9 cm? (a) No (b) Yes
  19. 19.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)?
  20. 20.The two shorter sides of a right-angled triangle are 12 cm and 5 cm. How long is the longest side (in cm)?
  21. 21.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  22. 22.An exterior angle of a triangle is 109°. One of its two interior opposite angles is 43°. What is the other one (in degrees)?
  23. 23.The longest side of a right-angled triangle is 17 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  24. 24.An exterior angle of a triangle is 67°. One of its two interior opposite angles is 20°. What is the other one (in degrees)?
  25. 25.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)?
  26. 26.An exterior angle of a triangle is 70°. One of its two interior opposite angles is 23°. What is the other one (in degrees)?
  27. 27.In an isosceles triangle, the two equal angles are 77° each. What is the third angle (in degrees)?
  28. 28.In an isosceles triangle, the two equal angles are 25° each. What is the third angle (in degrees)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 104°. What is each of the other two angles (in degrees)?
  30. 30.In triangle ABC, angle A = 90° and angle B = 22°. What is angle C (in degrees)?
  31. 31.The two interior opposite angles of a triangle are 46° and 53°. What is the exterior angle (in degrees)?
  32. 32.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  33. 33.In an isosceles triangle, the two equal angles are 41° each. What is the third angle (in degrees)?
  34. 34.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  35. 35.Can a triangle have sides of 8 cm, 14 cm and 2 cm? (a) No (b) Yes
  36. 36.In an isosceles triangle, the two equal angles are 48° each. What is the third angle (in degrees)?
  37. 37.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  38. 38.Can a triangle have sides of 4 cm, 7 cm and 6 cm? (a) Yes (b) No
  39. 39.In an isosceles triangle, the angle between the two equal sides is 140°. What is each of the other two angles (in degrees)?
  40. 40.An exterior angle of a triangle is 103°. One of its two interior opposite angles is 36°. What is the other one (in degrees)?

Answer key

  1. 30
  2. 23
  3. 18
  4. 132
  5. 25
  6. 15
  7. 55
  8. 13
  9. 72
  10. 35
  11. 46
  12. 36
  13. 19
  14. 53
  15. 140
  16. 45
  17. 19
  18. Yes
  19. 36
  20. 13
  21. 17
  22. 66
  23. 8
  24. 47
  25. 16
  26. 47
  27. 26
  28. 130
  29. 38
  30. 68
  31. 99
  32. 72
  33. 98
  34. 90
  35. No
  36. 84
  37. 72
  38. Yes
  39. 20
  40. 67

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