SOLUTION: I have to take a placement test for college for Algebra and the question I am having problems with is this . . . "What is the equation of the line that contains the points with (x,

Question 6477: I have to take a placement test for college for Algebra and the question I am having problems with is this . . . "What is the equation of the line that contains the points with (x,y) coordinates (-3,7) and (5,-1)? I know that the answer to the problem is y = -x+4. I cannot remember from High School which formula to use to solve the problem. Please help. Thank You!
J from Georgia
Answer by rapaljer(4671) (Show Source): You can put this solution on YOUR website!
First step is to find the slope between the two points.

In this case,

There are two ways to find the equation of a line given a point and a slope. This may NOT be the way you learned it, but I think the easiest way is to write the formula , which contains a total of 4 unknowns: y, x, m, and b, of which you know three of them--all but b, which you will need to find. You know that m = -1, and you know a point (choose either point, say the first point): x=-3 and y=7. So substitute all three numbers into the equation:

and solve for b:

So the equation of the line is
where x and y are variables and m= -1 and y = 4:

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