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Math Help - Y=3x-1?

  1. #1
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    Y=3x-1?

    hi i not too sure how to draw Y=3x-1!?!?
    would i draw it like this?

    Y=3x-1?-11.jpg
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  2. #2
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    Quote Originally Posted by andyboy179 View Post
    hi i not too sure how to draw Y=3x-1!?!?
    would i draw it like this?

    Click image for larger version. 

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    Dear andyboy179,

    Note that, when y=0\Rightarrow{x=\frac{1}{3}} Therefore your x intersect is incorrect.
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  3. #3
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    Quote Originally Posted by Sudharaka View Post
    Dear andyboy179,

    Note that, when y=0\Rightarrow{x=\frac{1}{3}} Therefore your x intersect is incorrect.
    where would it go??
    Last edited by andyboy179; September 10th 2010 at 07:26 AM. Reason: typo
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  4. #4
    A riddle wrapped in an enigma
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    Hi andyboy179,

    Your slope is 3.

    From your y-intercept of -1, move up 3 units and right 1 unit. You should arrive at ((1, 2). Then redraw your line.
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  5. #5
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    Quote Originally Posted by masters View Post
    Hi andyboy179,

    Your slope is 3.

    From your y-intercept of -1, move up 3 units and right 1 unit. You should arrive at ((1, 2). Then redraw your line.
    thanks! so on this question:
    x + 2y=6 how would i do this?? would it be:
    Y=3x-1?-11.jpg
    ?
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  6. #6
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    or would it be:
    Y=3x-1?-11.jpg
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  7. #7
    MHF Contributor ebaines's Avatar
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    Quote Originally Posted by andyboy179 View Post
    thanks! so on this question:
    x + 2y=6 how would i do this?? would it be:
    Click image for larger version. 

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    ?
    First thing to do is rearrange the equation so it is in the form y = mx+b, because that will tell you the slope (m) and the y-intercept (b):

    x+2y = 6
    2y = -x + 6
    y = -1/2 x +3

    From this you can see that the y-intercept is at 3 (not 2 like you have it inyour sketch), and the slope is -1/2. You can also determine the x-intercept by setting y =0, and you see that the x-intercept is at x= 6.
    Last edited by ebaines; September 10th 2010 at 08:28 AM.
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  8. #8
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    Quote Originally Posted by ebaines View Post
    First ting to do is reatrrange the equation so it is in the form y = mx+b, because that will tell you the slope (m) and the y-intercept (b):

    x+2y = 6
    2y = -x + 6
    y = -1/2 x +3

    From this you can see that the y-intercept is at 3 (not 2 like you have it inyour sketch), and the slope is -1/2. You can also determine the x-intercept by setting y =0, and you see that the x-intercept is at x= 6.
    thanks, i think im starting to understand it a bit better now!
    so for this one:
    Y= -2x-1
    would it be:
    Y=3x-1?-11.jpg
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  9. #9
    MHF Contributor ebaines's Avatar
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    Quote Originally Posted by andyboy179 View Post
    thanks, i think im starting to understand it a bit better now!
    so for this one:
    Y= -2x-1
    would it be:
    Click image for larger version. 

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    No - the y-intercept is at -1 (not positive 1 like you have it), and the slope is -2 (not positive 1/2).

    Last edited by ebaines; September 10th 2010 at 09:41 AM.
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  10. #10
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    can you explain how to find out where you plot the points because im getting lost!?
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  11. #11
    MHF Contributor ebaines's Avatar
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    I just edited my previous post to add a figure - maybe that will help.

    Start by plotting the y-intercept, which in this case is -1. So plot the point (0,-1). Since the slope is -2, starting from the y-intercept count 2 units up (positive y direction) and 1 unit to the left (negative x direction). This puts you at the point (-1,1). Now draw a straight line through these 2 points. The only "trick" here is to remember that the definition of "slope" is "rise over run," which is a measure of how fast the line rises. A negative slope means the line rises up to the left, and a positive slope means it rises up to the right. As a check, you can calculate the x-intercept (the point onteh line where y = 0): 0 = -2x-1, so x =-1/2. Now see if the point (-1/2, 0) is on the line you just plotted - if it is, then life is good.
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  12. #12
    Senior Member yeKciM's Avatar
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    Quote Originally Posted by andyboy179 View Post
    hi i not too sure how to draw Y=3x-1!?!?
    would i draw it like this?

    Click image for larger version. 

Name:	11.jpg 
Views:	67 
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ID:	18873


    to correctly draw line do this let's say you have equation of the line as yours y=3x-1

    you need just 2 points (any points) to draw the line

    let's make "table"

    let's say that x=0 . because of the equation y=3x-1 implies that y=3*0-1 = -1 . now you have one point M(x=0, y=-1) == M(0,-1) now we need one more let's say now that x=1 so put x=1 to equation and you get y=3*1-1 = 2 now you have second point N(1,2) just now connect those two lines and you have correctly drawn line

    P.S. doesn't matter which value of x are you chose it could be x= 10 -> y= 3*10-1 = 29 and x=-10 -> y= 3*(-10)-1 = -31 and again you have two points M(10,29) N(-10,-31) and again just connect those two points and you will get the same line
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