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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 694 · 40 sums
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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 two equal angles are 76° each. What is the third angle (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 75°. What is the third angle (in degrees)?
  3. 3.The longest side of a right-angled triangle is 20 cm and one of the other sides is 16 cm. How long is the third side (in cm)?
  4. 4.In triangle ABC, angle A = 88° and angle B = 57°. What is angle C (in degrees)?
  5. 5.In an isosceles triangle, the angle between the two equal sides is 50°. What is each of the other two angles (in degrees)?
  6. 6.In an isosceles triangle, the two equal angles are 55° each. What is the third angle (in degrees)?
  7. 7.In a right-angled triangle, one of the other two angles is 61°. What is the third angle (in degrees)?
  8. 8.An exterior angle of a triangle is 139°. One of its two interior opposite angles is 60°. What is the other one (in degrees)?
  9. 9.Can a triangle have sides of 6 cm, 6 cm and 12 cm? (a) No (b) Yes
  10. 10.In a right-angled triangle, one of the other two angles is 45°. What is the third angle (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 35°. What is the third angle (in degrees)?
  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.In an isosceles triangle, the angle between the two equal sides is 140°. What is each of the other two angles (in degrees)?
  14. 14.An exterior angle of a triangle is 68°. One of its two interior opposite angles is 46°. What is the other one (in degrees)?
  15. 15.In an isosceles triangle, the two equal angles are 64° each. What is the third angle (in degrees)?
  16. 16.Can a triangle have sides of 9 cm, 4 cm and 9 cm? (a) Yes (b) No
  17. 17.The two interior opposite angles of a triangle are 80° and 43°. What is the exterior angle (in degrees)?
  18. 18.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  19. 19.Can a triangle have sides of 3 cm, 12 cm and 4 cm? (a) No (b) Yes
  20. 20.In triangle ABC, angle A = 79° and angle B = 77°. What is angle C (in degrees)?
  21. 21.An exterior angle of a triangle is 94°. One of its two interior opposite angles is 68°. What is the other one (in degrees)?
  22. 22.In triangle ABC, angle A = 26° and angle B = 39°. What is angle C (in degrees)?
  23. 23.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  24. 24.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  25. 25.In an isosceles triangle, the angle between the two equal sides is 104°. What is each of the other two angles (in degrees)?
  26. 26.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  27. 27.The two interior opposite angles of a triangle are 22° and 20°. What is the exterior angle (in degrees)?
  28. 28.In an isosceles triangle, the angle between the two equal sides is 72°. What is each of the other two angles (in degrees)?
  29. 29.An exterior angle of a triangle is 112°. One of its two interior opposite angles is 75°. What is the other one (in degrees)?
  30. 30.An exterior angle of a triangle is 93°. One of its two interior opposite angles is 68°. What is the other one (in degrees)?
  31. 31.An exterior angle of a triangle is 64°. One of its two interior opposite angles is 40°. What is the other one (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 59° and 61°. What is the exterior angle (in degrees)?
  34. 34.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  35. 35.In triangle ABC, angle A = 72° and angle B = 33°. What is angle C (in degrees)?
  36. 36.In triangle ABC, angle A = 34° and angle B = 52°. What is angle C (in degrees)?
  37. 37.In triangle ABC, angle A = 32° and angle B = 34°. What is angle C (in degrees)?
  38. 38.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  39. 39.An exterior angle of a triangle is 130°. One of its two interior opposite angles is 70°. What is the other one (in degrees)?
  40. 40.Can a triangle have sides of 5 cm, 8 cm and 11 cm? (a) Yes (b) No

Answer key

  1. 28
  2. 15
  3. 12
  4. 35
  5. 65
  6. 70
  7. 29
  8. 79
  9. No
  10. 45
  11. 55
  12. 17
  13. 20
  14. 22
  15. 52
  16. Yes
  17. 123
  18. 50
  19. No
  20. 24
  21. 26
  22. 115
  23. 75
  24. 90
  25. 38
  26. 79
  27. 42
  28. 54
  29. 37
  30. 25
  31. 24
  32. 35
  33. 120
  34. 25
  35. 75
  36. 94
  37. 114
  38. 72
  39. 60
  40. Yes

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