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In the last lesson, I showed you how to get the equation of a line given a point and a slope using the formula

y - y1 = m ( x - x1 )

Anytime we need to get the equation of a line, we need two things

1   a point 

2

a slope

ALWAYS!

So, what do we do if we are just given two points and no slope?

No problem -- we'll just use the two points to pop the slope using this guy:

m = ( y2 - y1 ) / ( x2 - x1 )

Check it out:

Let's find the equation of the line that passes through the points

( 1 , 3 ) and ( -2 , 5 )

This one's a two-stepper...

STEP 1:  Find the slope

m = ( y2 - y1 ) / ( x2 - x1 ) = ( 5 - 3 ) / ( -2 - 1 ) = 2 / -3 = -2 / 3