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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 647 · 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 two equal angles are 80° each. What is the third angle (in degrees)?
  2. 2.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  3. 3.In triangle ABC, angle A = 87° and angle B = 23°. What is angle C (in degrees)?
  4. 4.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)?
  5. 5.In triangle ABC, angle A = 25° and angle B = 125°. What is angle C (in degrees)?
  6. 6.Can a triangle have sides of 19 cm, 4 cm and 10 cm? (a) Yes (b) No
  7. 7.An exterior angle of a triangle is 124°. One of its two interior opposite angles is 69°. What is the other one (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 46°. What is the third angle (in degrees)?
  9. 9.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  10. 10.In an isosceles triangle, the angle between the two equal sides is 140°. What is each of the other two angles (in degrees)?
  11. 11.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)?
  12. 12.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  13. 13.In triangle ABC, angle A = 51° and angle B = 92°. What is angle C (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 78°. What is the third angle (in degrees)?
  16. 16.The two interior opposite angles of a triangle are 63° and 42°. What is the exterior angle (in degrees)?
  17. 17.In triangle ABC, angle A = 65° and angle B = 50°. What is angle C (in degrees)?
  18. 18.The two shorter sides of a right-angled triangle are 3 cm and 4 cm. How long is the longest side (in cm)?
  19. 19.In an isosceles triangle, the two equal angles are 41° each. What is the third angle (in degrees)?
  20. 20.In triangle ABC, angle A = 44° and angle B = 66°. What is angle C (in degrees)?
  21. 21.In an isosceles triangle, the two equal angles are 73° each. What is the third angle (in degrees)?
  22. 22.An exterior angle of a triangle is 119°. One of its two interior opposite angles is 62°. What is the other one (in degrees)?
  23. 23.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  24. 24.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  25. 25.In triangle ABC, angle A = 37° and angle B = 34°. What is angle C (in degrees)?
  26. 26.In triangle ABC, angle A = 33° and angle B = 20°. What is angle C (in degrees)?
  27. 27.In triangle ABC, angle A = 73° and angle B = 23°. What is angle C (in degrees)?
  28. 28.The two shorter sides of a right-angled triangle are 9 cm and 12 cm. How long is the longest side (in cm)?
  29. 29.Can a triangle have sides of 11 cm, 14 cm and 2 cm? (a) Yes (b) No
  30. 30.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  31. 31.An exterior angle of a triangle is 99°. One of its two interior opposite angles is 51°. What is the other one (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 47°. What is the third angle (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 67° and 34°. What is the exterior angle (in degrees)?
  34. 34.The two interior opposite angles of a triangle are 75° and 37°. What is the exterior angle (in degrees)?
  35. 35.Can a triangle have sides of 8 cm, 8 cm and 18 cm? (a) Yes (b) No
  36. 36.In triangle ABC, angle A = 43° and angle B = 106°. What is angle C (in degrees)?
  37. 37.An exterior angle of a triangle is 110°. One of its two interior opposite angles is 55°. What is the other one (in degrees)?
  38. 38.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  39. 39.In an isosceles triangle, the angle between the two equal sides is 76°. What is each of the other two angles (in degrees)?
  40. 40.In triangle ABC, angle A = 35° and angle B = 113°. What is angle C (in degrees)?

Answer key

  1. 20
  2. 120
  3. 70
  4. 24
  5. 30
  6. No
  7. 55
  8. 44
  9. 45
  10. 20
  11. 15
  12. 30
  13. 37
  14. 78
  15. 12
  16. 105
  17. 65
  18. 5
  19. 98
  20. 70
  21. 34
  22. 57
  23. 20
  24. 20
  25. 109
  26. 127
  27. 84
  28. 15
  29. No
  30. 36
  31. 48
  32. 43
  33. 101
  34. 112
  35. No
  36. 31
  37. 55
  38. 17
  39. 52
  40. 32

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