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
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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.