SOLUTION: Write the equation of a line that passes through (-9, 7) and (9, -1)

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Question 1099484: Write the equation of a line that passes through (-9, 7) and (9, -1)
Found 2 solutions by josgarithmetic, Edwin McCravy:
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
m=%287-%28-1%29%29%2F%28-9-9%29=8%2F%28-18%29
m=-4%2F9


Pick (9,-1).
y-%28-1%29=-%284%2F9%29%28x-9%29
y%2B1=%28-4%2F9%29x%2B4
highlight%28y=-4x%2F9%2B3%29

Answer by Edwin McCravy(20055) About Me  (Show Source):
You can put this solution on YOUR website!
First use the slope formula:
m%22%22=%22%22%28y%5B2%5D-y%5B1%5D%29%2F%28x%5B2%5D-x%5B1%5D%29
where (x1,y1) = (-9,7)
and where (x2,y2) = (9,-1)

m%22%22=%22%22%28%28-1%29-%287%29%29%2F%28%289%29-%28-9%29%29

m%22%22=%22%22%28-8%29%2F%289%2B9%29

m%22%22=%22%22%28-8%29%2F18

m%22%22=%22%22-4%2F9

Now that you have the slope, use the point-slope formula:

y-y%5B1%5D%22%22=%22%22m%28x-x%5B1%5D%29

where (x1,y1) = (-9,7)

[Don't substitute anything for variables x and y, but leave them
as they are and just substitute for x1 and y1.]

y-y%5B1%5D%22%22=%22%22m%2A%28x-x%5B1%5D%29
y-7%22%22=%22%22expr%28-4%2F9%29%2A%28x-%28-9%29%29
y-7%22%22=%22%22expr%28-4%2F9%29%2A%28x%2B9%29
y-7%22%22=%22%22expr%28-4%2F9%29%2Ax-4
y%22%22=%22%22expr%28-4%2F9%29%2Ax%2B3

That's the slope y-intercept form.  If
you like you can get it into general form.
Multiply through by 9 to clear the fraction:

9y%22%22=%22%22-4x%2B27

4x%2B9y%22%22=%22%2227

Edwin