SOLUTION: find n such that the slope of the line containing (7,-12) and (n n+4) is parallel to 2x+y+8

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Question 678935: find n such that the slope of the line containing (7,-12) and (n n+4) is parallel to 2x+y+8
Answer by ReadingBoosters(3246) About Me  (Show Source):
You can put this solution on YOUR website!
Start with 2x+y+8, is this 2x+y+8=0 or 2x+y=8 ???
y = -2x-8
Therefore, the slope is -2
...
A parallel line will have the SAME slope
...
Using the point(7,-12) and the determined slope apply point slope formula
y--12 = -2(x-7)
y+12 = -2(x-7)
y+12 = -2x+14
y = -2x + 14 - 12
y = -2x + 2
...
Applying the n variable point
n+4 = -2n + 2
solve for n
n + 2n = 2 - 4
3n = -2
n = -2%2F3
...
Alternatively, applying the slope formula
%28-12-%28n%2B4%29%29%2F%287-n%29+=+-2%2F1
%28-12-n-4%29%2F%287-n%29+=+-2%2F1
%28-16-n%29%2F%287-n%29+=+-2%2F1
cross multiply
(-16-n) = -2(7-n)
-16 - n = -14 + 2n
solve for n
-16 + 14 = 2n + n
-2 = 3n
n = -2%2F3
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