y = mx + b
The formula y = mx + b which is explained on this page, is used in mathematics to describe a linear equation (a straight line). This page contains an explanation about it and provides some exercises in order to get familiar with the formula.

y = mx + b

m is the
[
slope
]
of the line
b is the value of y at x = 0; the line crosses the y axis at y = b.

Exercises
  1. The slope of a line is 4/3, at the y intercept y = 6. Give the formula.
  2. Determine the value of this function at x = 12?
  3. Some line intercepts the y axis at y = 3. At x = 18 it has climbed to y = 5. Write this in the form y = mx + b.
  4. According to the formula you calculated, what is the value of x at y = 39?
  5. Point W(-7,3) is connected to the origin of the coordinate system trough a straight line. Give the formula.
Solutions
  1. m = 4/3
    b = 6
    y = (4/3)x + 6
  2. y = (4/3)*12 + 6 = 22
  3. b = 3
    m = Δy/Δx = 2/18 = 1/9
    y = (1/9)x + 3
  4. 39 = (1/9)x + 3
    (1/9)x = 36
    x = 324
  5. W(-7,3), O(0,0)
    Δx = 0 - -7 = 7
    Δy = 0 - 3 = -3
    m = -3/7
    b = 0
    y = (-3/7)x

Now you should be able to graph a linear equation once the formula of the function is known, or write the equation down when you see the graph. Note: In some countries the formula y = mx + b is known as y = mx + c or as y = ax + b.