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Math Help - Finding point of intersection

  1. #1
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    Finding point of intersection

    I have been asked to draw a graph of the line that passes through the point (-4, -2) and has a gradient of 2!

    Have done that

    Next question is Find the point of intersection of the above line with the line y = -x + 2

    How do i go about doing that? can someone please explain? Do i need to do a table of values?
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  2. #2
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    Quote Originally Posted by BsMummy View Post
    I have been asked to draw a graph of the line that passes through the point (-4, -2) and has a gradient of 2!

    Have done that

    Next question is Find the point of intersection of the above line with the line y = -x + 2

    How do i go about doing that? can someone please explain? Do i need to do a table of values?
    To make a table of values, you have to know the equation. You are only given a point, and a gradient. This means you must derive the equation. If the gradient is 2, then we can use the equation y=mx+b to write:

    y=2x+b

    You know that the point (-4,-2) is on the line. This means that:

    -2=2(-4)+b

    Sovling for b:

    b=6

    The equation of the line can now be written.

    y=2x+6

    To find the point where the lines intersect, you have to solve the system of equations:

    y=2x+6
    y=-x+2

    The solutions for x and y will give the point of intersection.
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  3. #3
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    Oh, I forgot that you need to graph the line to. To draw the graph, find the y-intercept by seting x=0.

    y=2x+6
    y=6 is the y intercept, which is the point (0,6).

    You were already given another point on the line in the statement of the problem. Plot that point, and the y-intercept, and then draw the line through those points.
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  4. #4
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    im dumb and all that has gone way over my head! also i thought it was
    y = mx+c - or is that the same as y = mx+b?
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  5. #5
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    Quote Originally Posted by BsMummy View Post
    im dumb and all that has gone way over my head! also i thought it was
    y = mx+c - or is that the same as y = mx+b?
    That is exactly the same, just a different name for the variable.
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  6. #6
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    Quote Originally Posted by BsMummy View Post
    im dumb and all that has gone way over my head! also i thought it was
    y = mx+c - or is that the same as y = mx+b?
    Ok, it sounds like you need an much more involved tutorial on this subject.

    This video will help you understand how to find the equation of a line when you are given the slope and a point. Write down what I showed you above, and compare that to what they do in the video.



    This video will help you graph the line:


    good luck
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