The equation of a straight line is given on the right. In this equation:
Each of these will be defined below. (NOTE: The equation of a line is frequently shown as y = m x + b.) 

Let's label the equation for our pizza example. The slope of the line tells us how much the cost of a pizza changes as the number of toppings change 

As you found in an earlier unit of this tutorial, the
equation for our pizza example is:
The slope in our pizza example is .75 (75 cents). In any equation
of a straight line, the slope of the line is the constant that
is multiplied by the x variable. (If you wish to review
the definitions of constants and variables, return to the first unit.)
In the equation y = a + b x, the constant labeled "a" is what is called the yintercept. The yintercept is the point at which the line crosses the yaxis. The yintercept is the value of y when x is equal to zero. Note that if x = 0, then y = a. When we use graphs, we call this point (0, a) the yintercept. 

In our pizza example, the equation of the relationship is given by: The yintercept occurs when there are no additional toppings (x = 0), which is the price of a plain pizza, or $7.00. As you can see, the point where the line crosses the yaxis is (0, 7). The yintercept in this case is 7. 

Now, let's look at a few more examples. In these we are simply trying to determine the slope and yintercept from the equation of a line.
Determine the slope and yintercept for the line given by each equation.
y = 20 + 30 x y intercept is 20
slope is 30y = 4  10 x y intercept is 4
slope is (10)y = .5 x + .66 y intercept is .66
slope is .5
When you are sure you understand how to determine the yintercept and slope of a line from its equation, do the practice exercise below.
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