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Math Help - Graphs using slope and y intercept

  1. #1
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    Graphs using slope and y intercept

    I'm just going to link a picture to the question in my book since I have no idea how I would even attempt to draw a graph on here manually.

    Basically, I don't understand why in the equation "y = -2/3x - 3" when they go to plot it on the graph, they're making the -3 a positive 3 instead, and there are other parts in the book that have a similar equation where both the slope and the y intercept are negatives, but they use both as positives when turning it into the graph portion, and I really don't understand why.

    Any help would be much appreciated in understanding why that is.



    mathproblem_zpsa6456c35.png Photo by Azuraiiii | Photobucket
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  2. #2
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    Re: Graphs using slope and y intercept

    I plotted y = -\displaystyle\frac{2}{3}x - 3 \slope on my 3D grapher and the line I got intercepted the y-axis at \slope -3 \slope not +3. The line they plotted in Photobucket is the equation \space y = -\displaystyle\frac{2}{3}x + 3. I would say that it is incorrect. Your y-intercept is clearly \slope -3.
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  3. #3
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    Re: Graphs using slope and y intercept

    there should be no confusion as far as slope intercept form is concerned. for the equation y = -2/3 x - 3, the y intercept is -3 and the coordinates of the point will be ( 0, -3 ). The slope is - 2/3 this one mas consider 9 -2 ) / 3 OR 2 / ( -3 ) and locate the next point and then draw the line. Anything otherwise would be wrong.
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  4. #4
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    Re: Graphs using slope and y intercept

    Thanks for the confirmations, I thought I was losing it for a second there.
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  5. #5
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    Re: Graphs using slope and y intercept

    Strange, but Wolfram Alpha agrees with your book. http://www.wolframalpha.com/input/?t=crmtb01&f=ob&i=plot%20-(2%2F3)%20x%20-3
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  6. #6
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    Re: Graphs using slope and y intercept

    Nooo, why did you have to say that, now I'm back to questioning myself again!
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  7. #7
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    Re: Graphs using slope and y intercept

    Quote Originally Posted by ReneG View Post

    the second graph is correct. If you notice on the first graph, the y-axis is not at the origin.
    Last edited by jpritch422; June 27th 2013 at 06:12 AM.
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