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Math Help - some y=mx+b help?

  1. #1
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    some y=mx+b help?

    okay well i have some algebra homework to do and there are a couple things that have me confused. you see, in this section of our book we are finding slope and y-intercepts, as well as graphing them. i could do just fine if they're already in slope-intercept form, but im having trouble changing a few of them. for example:

    y=3x+1

    this is easy, as the slope is right there. slope is 3. and y-intercept is 1. and some problems like this:

    y-9x=0

    i could put that into slope intercept form without major complications.

    y-9x=0
    +9x +9x

    the -9x and the +9x cancel eachother out, and you have to do the same thing to the other side. so it's now changed to:

    y=9x

    because the 0 is understood in that. so slope is 9 and intercept is 0 or the origin. but im kind of lost for a couple of these:

    3x+4y=16

    y= 6-x
    3
    for the first one, im not sure if you would want to:

    3x+4y=16
    -3x -3x

    4y=16-3x
    (i also dont know if you'd write it as 4y=3x-16 or 4y=16-3x)

    or if you'd want to:

    3x+4y=16
    4 4

    in this, the four would cancel out on the y side and just divide as usual on the other side, making it:

    3x+y=4

    and then you'd subtract the 3x on both sides.

    or does that order even matter?

    and on the other one:

    y=6-x
    3

    im just lost on that one. i tried looking back in the book and i can't really find any help for those.

    so is there anybody out there who could tell me what exactly to do in these problems? thanks!
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  2. #2
    Super Member craig's Avatar
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    Quote Originally Posted by bespinboy View Post
    3x+4y=16
    3x+4y=16

    Subtract 3x from both sides, 4y=-3x + 16.

    Divide through by 4, y=\frac{-3}{4}x + 4.

    There you have your equation in the form you have above.

    Gradient of \frac{-3}{4} and intercept of 4.
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  3. #3
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    thanks craig!
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  4. #4
    Super Member craig's Avatar
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    How did you manage with the second question did that go ok?
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