SOLUTION: If the line containing the points (-8,m) and (2,1) is parallel to the line containing the points (11,-1) and (7,m+1), what is the value of m?

Algebra ->  Algebra  -> Coordinate-system -> SOLUTION: If the line containing the points (-8,m) and (2,1) is parallel to the line containing the points (11,-1) and (7,m+1), what is the value of m?      Log On

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Question 63532: If the line containing the points (-8,m) and (2,1) is parallel to the line containing the points (11,-1) and (7,m+1), what is the value of m?
Answer by ankor@dixie-net.com(12701) About Me  (Show Source):
You can put this solution on YOUR website!
If the line containing the points (-8,m) and (2,1) is parallel to the line containing the points (11,-1) and (7,m+1), what is the value of m?
:
We know that the slope = (y2-y1)/(x2-x) and parallel lines have equal slopes:
Slope 1 = Slope 2
%281-m%29%2F%282-%28-8%29%29 = %28%28m%2B1%29-%28-1%29%29%2F%287-11%29
:
%281-m%29%2F%282%2B8%29 = %28m%2B1+%2B+1%29%2F%287-11%29
:
%281-m%29%2F10 = %28m%2B2%29%2F%28-4%29
:
Cross multiply and solve for m:
10(m+2) = -4(1-m)
10m + 20 = -4 + 4m
10m -4m = -4 - 20
6m = - 24
m =-24/6
m = -4
:
:
Check to see if they have the same slopes, substitute -4 for m
%281-m%29%2F%282-%28-8%29%29 = %28%28m%2B1%29-%28-1%29%29%2F%287-11%29
:
%281-%28-4%29%29%2F%282-%28-8%29%29 = %28%28-4%2B1%29-%28-1%29%29%2F%287-11%29
:
%28%2B5%29%2F%28%2B10%29 = %28%28-3%29%2B+1%29%2F%28-4%29
:
%28%2B5%29%2F%28%2B10%29 = %28-2%29%2F%28-4%29
;
Both slopes are +(1/2)
:
Make sense to you?