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Math Help - equation of a straight line through A(-1,3) perpendicular to y=1/3x-1?

  1. #1
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    equation of a straight line through A(-1,3) perpendicular to y=1/3x-1?

    hi,

    im not too sure how to work this out:

    equation of a straight line through A(-1,3) perpendicular to y=1/3x-1

    i require some help on this one step at a time please.

    thanks!
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  2. #2
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    Re: equation of a straight line through A(-1,3) perpendicular to y=1/3x-1?

    Quote Originally Posted by andyboy179 View Post
    hi,

    im not too sure how to work this out:

    equation of a straight line through A(-1,3) perpendicular to y=1/3x-1

    i require some help on this one step at a time please.

    thanks!
    1. Two lines with the slopes m_1 and m_2 are perpendicular if the slopes satisfy the equation


    m_1 \cdot m_2 = -1

    So the slope of the perpendicular line is (-3).

    2. Use the point-slope-formula of a straight line to determine the equation of the line in question:

    y-y_1 = m(x-x_1)

    where x_1, y_1 are the coordinates of the point which is located on the line:

    y-3=(-3)(x-(-1))~\implies~y=-3x
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  3. #3
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    Re: equation of a straight line through A(-1,3) perpendicular to y=1/3x-1?

    Quote Originally Posted by andyboy179 View Post
    equation of a straight line through A(-1,3) perpendicular to y=1/3x-1
    I have already essentially answered this here.

    So applying that to this we get y=-3x+~?
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  4. #4
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    Re: equation of a straight line through A(-1,3) perpendicular to y=1/3x-1?

    Hi andyboy179.
    The slope of the line perpendicular to y=1/3 x -1 is -3because the product of the slopes must be -1. Use the point slope formula to find the new line

    y-3/x+1 = -3 finish it


    bjh
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  5. #5
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    Re: equation of a straight line through A(-1,3) perpendicular to y=1/3x-1?

    y=x+1?
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    Re: equation of a straight line through A(-1,3) perpendicular to y=1/3x-1?

    Quote Originally Posted by Plato View Post
    I have already essentially answered this here.

    So applying that to this we get y=-3x+~?
    but if you look on that link i don't understand it!!!
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  7. #7
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    Re: equation of a straight line through A(-1,3) perpendicular to y=1/3x-1?

    actually would it be y=-3+4?
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  8. #8
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    Re: equation of a straight line through A(-1,3) perpendicular to y=1/3x-1?

    You have the line: y=-3x+?, now you have also a point A(-1,3) on the straight line so you have to fill in the coordinates in the general equation:
    3=-3(-1)+? ...
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