Every straight
line can be represented by an equation: y = mx + b. The coordinates of every
point on the line will solve the equation if you substitute them in the equation
for x and y.

The slope
*m* of this line - its steepness, or slant - can be calculated like this:

*
m* = __change in y-value__

change
in x-value

The
equation of any straight line, called a linear
equation, can be written as: y = *m*x + b, where *m*
is the slope of the line and b is the y-intercept.

The
y-intercept
of this line is the value of y at the point where the line crosses the y axis.