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Math Help - x and y intercept graphs

  1. #1
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    x and y intercept graphs

    i need help on these problems, they dont make sence to me, and i have to get this finished pretty fast, can anyone help me please? appreciate it much

    1. y=x/3
    2. y=-3x-2
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  2. #2
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    Just what are you trying to accomplish?

    1. y=x/3
    2. y=-3x-2

    Two linear equations (i.e., their graphs are straight lines).

    y = mx + b is the most common form you will see.
    m is the slope or "rise over run".
    b is the y-intercept or where the graph crosses the y-axis when x = 0.

    [1] m = 1/3, b = 0
    [2] m = -3, b = -2

    The slope can be determined by use two points (x1, y1), (x2, y2):
    (y2 - y1) / (x2 - x1)

    Want more?

    Think of the Pythaorean Theorem: c^2 = a^2 + b^2 where (c) is the length of a hypotenuse (the longest side) of a right triangle, and (a) and (b) are the lengths of the other two sides.

    Form this information you can also derive the distance formula (point-to-point on a graph), the midpoint formula, and the slope of a line.

    It is a good mnemonic device.

    The slope is also the "tangent" to the angle opposite the right angle if you use the two points as two ends of the diagonal of a right triangle, and then draw the rest of a right triangle using that diagonal.

    That may sound complicated, but a picture would make it very clear. By the time I downloaded a picture, you may have already drawn a right triangle for yourself.

    One of these days this information about a right triangle will ease your understanding when you get into differential calculus.
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  3. #3
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    yeah both of the problems are straight lines i know that, but i gotta find the coordinates to make the straight line on the grid

    1. y=1/3 coordinate 1: x=0 y=? coordinate 2: x=? y=0

    2. y=-3x-2 coordinate 1: x=0 y=-2 coordinate 2: x=? y=0
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  4. #4
    Rhymes with Orange Chris L T521's Avatar
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    Quote Originally Posted by nightmare1593 View Post
    i need help on these problems, they dont make sence to me, and i have to get this finished pretty fast, can anyone help me please? appreciate it much

    1. y=x/3
    2. y=-3x-2
    For #1, to find the x intercept, set y=0:

    0=\frac{1}{3}x \implies \color{red}\boxed{x=0}

    to find the y intercept, set x=0:

    y=\frac{1}{3}(0) \implies \color{red}\boxed{y=0}

    Thus, the coordinates of the x intercept and y intercept are the same : \color{red}\boxed{(0,0)}.

    The graph below verifies our answer:



    For #2, to find the x intercept, set y=0:

    0=-3x-2 \implies \color{red}\boxed{x=-\frac{2}{3}}

    to find the y intercept, set x=0:

    y=-3(0)-2 \implies \color{red}\boxed{y=-2}.

    Thus, the x intercept is \color{red}\boxed{\left(-\frac{2}{3},0\right)} and the y intercept is \color{red}\boxed{(0,-2)}

    The graph below verifies our answer.

    Last edited by Chris L T521; May 26th 2008 at 08:58 PM. Reason: typo
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