1. Make the line horizontal.
    What do you need to change to do this?

2. Work out the equation of this line.

3. Make the line vertical. 
    What is its gradient?

4. What do you think the equation 
    of the vertical line will be?

Equation of horizontal line

Show vertical line and equation

m = -5 (slider from -5 to 1000)
b = 0.1 (slider from -5 to 5)
f: y = (m * x) + b
text3: "y=" + b + ""
a = false
p = 4 (slider from -10 to 10)
g: x = p
text6: "x = " + p + ""
c = false