SOLUTION: The Compass practice test question is 'What is the equation of the line that contains the points with (x,y) coordinates (-3,7) and (5,-1')? I know the answer is y=x+4 but how do yo

Algebra ->  Linear-equations -> SOLUTION: The Compass practice test question is 'What is the equation of the line that contains the points with (x,y) coordinates (-3,7) and (5,-1')? I know the answer is y=x+4 but how do yo      Log On


   

Question 623042: The Compass practice test question is 'What is the equation of the line that contains the points with (x,y) coordinates (-3,7) and (5,-1')? I know the answer is y=x+4 but how do you go about getting that answer? Is there an easy formula to figure it out? Please show me step by step...
Answer by Earlsdon(6294) About Me  (Show Source):
You can put this solution on YOUR website!
Formula? No, I don't think so!
Here's one way to get the answer.
Start with:
y = mx+b Find the slope, m:
m+=+%28y%5B2%5D-y%5B1%5D%29%2F%28x%5B2%5D-x%5B1%5D%29 The x's and y's are the coordinates of the two given points, so we substitute:
m+=+%28-1-7%29%2F%285-%28-3%29%29 Evaluate.
m+=+%28-8%29%2F8
m+=+-1 so now you have:
y = -x+b To find b, substitute the x- and y-coordinates of either of the two given points. Let's choose (-3, 7) and substitute:
7 = -1(-3)+b Solve for b.
7 = 3+b Subtract 3 from both sides.
b = 4
The final equation is:
y = -x+4
Your answer is almost correct but you'll find that the slope, m, is negative!