SOLUTION: why are 3x+6y=12 and 6x-3y=9 parallel

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Question 551994: why are 3x+6y=12 and 6x-3y=9 parallel
Answer by neatmath(302) About Me  (Show Source):
You can put this solution on YOUR website!

In order to solve this question, we need to find the slopes and y-intercepts of the 2 lines.

We can easily do this by solving both equations in terms of y.

y=mx%2Bb where m is the slope, and b is they y-intercept.

First equation:

3x%2B6y=12

6y=-3x%2B12

y=-x%2F2%2B2

Next equation:

6x-3y=9

6x=3y%2B9

6x-9=3y

2x-3=y

y=2x-3

Well, we should now realize something important here.

These lines are NOT parallel, they are perpendicular!!!

If they were parallel, they would have the exact same slope (m), and would have different y-intercepts (b).

These lines have slopes (m) that are negative reciprocals.

When 2 lines have slopes that are negative reciprocals,

by definition, they are perpendicular.

If you sketch the lines, you will see that they are perpendicular, and not parallel to each other.

I hope this helps! :)

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