# Examples of the Two Points Form of the Equation of a Line

__Example 1__**:**

A milkman can sell 650 liters of milk at $3.15 per liter and 800 liters of milk at $3.00 per liter. Assuming the graph of the sale price and the milk sold to be a straight line, find the number of liters of milk that the milkman can sell at $2.50 per liter.

__Solution__**:**

Let be the number of liters of milk sold and be the price per liter. The given information can be written in the form of points and .

Since the graph of the sale price and the milk sold is a straight line, we find the equation of a straight line through the points and as follows:

Using the two points form of the equation of a straight line

In order to find the number of liters of milk that the milkman can sell at , we put in the above equation, and we get

This result shows that the milkman can sell 1301 liters of milk at $2.50 per liter.

__Example 2__**:**

Find the equation of straight line passing through the points and .

Consider the points and . Now using these points in the two point form of the equation of straight line, we get

This is the required equation of a straight line.