Finding the Equation of a Straight Line

Finding the Equation of a Straight Line-cont.

MathsDirect

Finding the equation from two points

Consider the line that passes through the points (2,2) and (5,1)

We can find the gradient of the line
We can now use this gradient, together with one the points, to find the equation		It is perfectly okay to leave the equation in this form, unless you where asked for an answer in the form y=mx+c.

This method can be summed up by the formula

The right hand side is just calculating the gradient.

Example - Find the equation of the line that passes through the points (-3,-2) and (2,5)

Substitute the numbers into the formula Simplify Cross multiply and tidy up

It does not matter which point you use on the left hand side. You end up with the same answer.