



 
Hi Conor, I am going to show you two ways to write the equation of a line through two points, but I am going to use the points (2, 2) and (4, 1). For each of the two methods I am going to illustrate I need the slope m of the line so I'm going to find it first. The expression I have seen in most books is that the slope m of the line containing the two points (x_{1}, y_{1}) and (x_{2}, y_{2}) is I think of it as "the difference between the ycoordinates divided by the difference between the xcoordinates". In my case I get (make sure you subtract the numerator and denominator in the same order) Expression 1:
Expression 2:
Now try your two points. Penny  


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