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Math Help - make y the subject 4x+3y+15

  1. #1
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    make y the subject 4x+3y+15

    this question has stumped me so can u plz help thanx :

    make y the subject 4x+3y+15
    Last edited by mr fantastic; April 30th 2009 at 03:26 AM. Reason: Copied post title into post
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  2. #2
    Super Member Gamma's Avatar
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    Make the subject

    Doesn't that just mean to solve for y?
    4x+3y+15=0
    3y=-(4x +15)
    y=\frac{-(4x +15)}{3}
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  3. #3
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    (4,y) (2,7) solve for y

    thanx man i got a bit stuck on another one
    (4,y) (2,7)
    you have to solve for y again by using the (x1 y1) (x2 y2) method and where m=y2-y1 over x2-x1 < thats a fraction hopefully u can help thanx
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  4. #4
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    You need to learn to write your problems out correctly. In your first post you wrote "make y the subject 4x+3y+15" which makes no sense- that is an expression, not an equation and has no "subject". Gamma assumed you mean 4x+ 3y+ 15= 0. If that was what you meant, you are lucky!

    Now you write "(4,y) (2,7)" and say "you have to solve for y again..." I think you mean that (4,y) and (2,7) are points some line must pass through. The slope of such a line would be \frac{y- 7}{4-2}= \frac{y- 7}{2} but unless you are given the slope to set that equal to, I see no equation to solve for y.
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  5. #5
    Super Member Gamma's Avatar
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    Yeah dude that was a shot in the dark. Same for this one, all I can hope is you mean.

    m=\frac{7-y}{2-4}=\frac{7-y}{-2}=-\frac{7}{2}+\frac{y}{2}

    Thus m+\frac{7}{2}=\frac{y}{2}

    y=2m+7
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