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Math Help - Graphs

  1. #1
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    Graphs

    Hey, i was asked to find the co-ordinates of the points were the graph, y=x^2-7x+6 crosses the axis, to find this i did x =1,2,3-1,-2 etc and found the y value. i got that (0,6)(1,0)(6,0) crossed, but this looks a little strnage to draw a curve on the graph.... have i done it right?

    Also what would be the best way of working out y=x(x-3)^2, so that i could sketch it?

    Thank you!
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  2. #2
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Chez_ View Post
    Hey, i was asked to find the co-ordinates of the points were the graph, y=x^2-7x+6 crosses the axis, to find this i did x =1,2,3-1,-2 etc and found the y value. i got that (0,6)(1,0)(6,0) crossed, but this looks a little strnage to draw a curve on the graph.... have i done it right?
    "...crosses the axis..." Not very specific. Given the rest of the post I imagine you are looking for both the x and y intercepts?

    -Dan
    Attached Thumbnails Attached Thumbnails Graphs-parabola.jpg  
    Last edited by topsquark; December 10th 2007 at 09:41 AM. Reason: Bah! I'm having a lousy afternoon!
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  3. #3
    Bar0n janvdl's Avatar
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    Quote Originally Posted by Chez_ View Post
    Hey, i was asked to find the co-ordinates of the points were the graph, y=x^2-7x+6 crosses the axis, to find this i did x =1,2,3-1,-2 etc and found the y value. i got that (0,6)(1,0)(6,0) crossed, but this looks a little strnage to draw a curve on the graph.... have i done it right?

    Also what would be the best way of working out y=x(x-3)^2, so that i could sketch it?

    Thank you!
    That graph will only have two x-intercepts...

    Find the values of x where y = 0

    0 = x^2 - 7x + 6

    0 = (x - 6)(x - 1)

    So \ x = 6 \ or \ x = 1
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  4. #4
    Bar0n janvdl's Avatar
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    Quote Originally Posted by topsquark View Post
    ...other x intercept is (-6, 0).

    -Dan
    (+6;0) Topsquark?
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  5. #5
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Chez_ View Post
    Also what would be the best way of working out y=x(x-3)^2, so that i could sketch it?
    The best way is to do it point by point, just like you did the other one. You know that the x intercepts are (0, 0) and (3, 0), and you know the y intercept is (0, 0). Now plot the points for, say x = -1, 1, 2, 4, and 5. Now connect the dots with a smooth curve.

    -Dan
    Attached Thumbnails Attached Thumbnails Graphs-cubic.jpg  
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  6. #6
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by janvdl View Post
    (+6;0) Topsquark?
    I think I'm having one of those days where I'm having one of those days. (Thank you.)

    -Dan
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  7. #7
    Bar0n janvdl's Avatar
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    Quote Originally Posted by topsquark View Post
    I think I'm having one of those days where I'm having one of those days. (Thank you.)

    -Dan
    Hehe, no problem. It happens to me a lot too. And it's usually the reason why i lose marks in exams or tests.
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  8. #8
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    eq of lines, graphs

    I have a picture of a line AB tht eq is y=4x-5 and passes through the point 9(2,3). The line BC is perp to AB and cuts the x axis at C. I need tofind the equation of line BC, which i have done, but i also need to find the x coordinate of C, but im not sure how do it? thnx

    Also how could i express 3(in a square root thing)
    --------
    6-3(3 again in sqr root thing)
    in the form of p+q 3(in sqroot)


    Iv now with the help of you great people being able to complete my practise paper and practised and found some new tips lol thnx
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  9. #9
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Chez_ View Post
    I have a picture of a line AB tht eq is y=4x-5 and passes through the point 9(2,3). The line BC is perp to AB and cuts the x axis at C. I need tofind the equation of line BC, which i have done, but i also need to find the x coordinate of C, but im not sure how do it? thnx

    Also how could i express 3(in a square root thing)
    --------
    6-3(3 again in sqr root thing)
    in the form of p+q 3(in sqroot)


    Iv now with the help of you great people being able to complete my practise paper and practised and found some new tips lol thnx
    I answered this as best as I could in your other thread.

    -Dan
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