18. A line perpendicular to the x-axis is a vertical line.
The equation of a vertical line is
x = k,
where k is the x-coordinate of every point on the line.
Since this vertical line goes through point (-10, 0.5), and this point has x-coordinate -10, then every point on the line has x-coordinate -10.
The equation is
x = -10
19.
[tex]f(x) = \dfrac{2}{3}x - 1 [/tex]
To find f(9), just replace x with 9 and evaluate the expression.
[tex]f(9) = \dfrac{2}{3} \times 9 - 1 [/tex]
[tex]f(9) = \dfrac{18}{3} - 1 [/tex]
[tex]f(9) = 6 - 1 [/tex]
[tex]f(9) = 5 [/tex]
20.
[tex] \sqrt{128} =[/tex]
[tex] = \sqrt{64 \times 2} [/tex]
[tex] = \sqrt{64} \times \sqrt{2} [/tex]
[tex] = 8 \times \sqrt{2} [/tex]
[tex] = 8 \sqrt{2} [/tex]
