silemus.
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  1. 1Angles in a triangle
  2. 2Exterior angle of a triangle
  3. 3Triangle angle sum
  4. 4Pythagorean theorem
  5. 5Pythagorean theorem
  6. 6Ladder, Pythagorean theorem
  7. 7Diagonal of a rectangle
  8. 8Similar triangles ratio
  9. 11Right triangle, Pythagoras
  10. 13Right triangle, find a leg
  11. 15Right triangle trig, finding angle A
  12. 16Arc length of a circle
  13. 17Area of a sector
  14. 20Tangent-radius right triangle
  15. 23Corresponding angles equal
  16. 24Co-interior angles sum to 180
  17. 25Vertical angles equation
  18. 27Regular polygon from angle
  19. 28Exterior angles of a pentagon
  20. 29Area of a trapezoid
  21. 32Volume of a cylinder
  22. 34Volume of a sphere
  23. 35Surface area of a sphere
  24. 36Distance between two points
  25. 37Midpoint of a segment
  26. 38Finding an endpoint from midpoint
  27. 39Line through two points

3Triangle angle sum

A triangle has angles x°, x° and (2x + 20)°. Find x.

The three angles must add to 180°, so x + x + (2x+20) = 180, giving 4x + 20 = 180, so x = 40. Check: 40 + 40 + 100 = 180.

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