18,19,20,21,23 me. i really need this answer. me.

18. Supplementary

19. Vertical

20. x = 7

23. x = 25

Step-by-step explanation:

Use angle relationships to make equations which you can solve for x.

Example:

18. These two angles form a line. These are called supplementary.

19. These angles are across a vertex from each other and are equal or the same.

20. 9x + 1 = 7x - 9 + 5x - 11

9x + 1 = 12x - 20

9x - 9x + 1 = 12x - 9x - 20

              1 = 3x - 20

      1 + 20 = 3x - 20 + 20

            21 = 3x

              7 = x

23. These two angles are across a vertex from each other. This means the angles are equal. Think of it as a reflection. If you folded the paper on that vertex, the lines would be in the exact same place.

So set the two expressions equal to each other. Then use inverse operations to isolate x and solve.

5x + 4 = 8x - 71

5x - 5x + 4 = 8x - 5x - 71

4 = 3x - 71

4 + 71 = 3x - 71 + 71

75 = 3x

25 = x