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Math Help - Find equation of a line perpendicular to something passing through something and some

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    Find equation of a line perpendicular to something passing through something and some

    Find equation of a line perpendicular to something passing through something and something?
    Please answer without the point slope formula I prefer the substitution method. I know how to find the equation of a line perpendicular to something passing through a given co ord but not something passing through 2 given co ords. Thanks, need this for my GCSE.
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    Re: Find equation of a line perpendicular to something passing through something and

    Sorry, but this is a bit confused. Perhaps if you define what you mean by all those "somethings" it would be clearer what you're asking. Are you asking about lines perpendicular to lines, or perpendicular to circles, or 3-dimensional surfaces, or what? By "point slope method" are you talking about how to find the equation of a line given two sets of coordinates? Finally what do you mean by finding a line perpendicular to "something ...passing through 2 given coordinates?" Perhaps if you gave an example we could be of better help.
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    Re: Find equation of a line perpendicular to something passing through something and

    Perpendicular to a given line.
    Yes, I am.
    Something 1 = equation of line
    Something 2&3 = set of coords

    find the equation of a line perpendicular to something 1 passing through something 2 and something 3
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    Re: Find equation of a line perpendicular to something passing through something and

    It makes no sense to say that a line "passes through" a set of coordinates. Passing through the x and y axes at given points? There exist a unique line passing through given point perpendicular to a given line. Is that what you mean? PLEASE tell us exactly what the problem you are trying to solve is.
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    Re: Find equation of a line perpendicular to something passing through something and

    Find the equation of a line perpendicular to y=4x+2 passing through (3,-5) and (4, 8)

    That is an example.
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    Re: Find equation of a line perpendicular to something passing through something and

    Quote Originally Posted by Ashir View Post
    Find the equation of a line perpendicular to y=4x+2 passing through (3,-5) and (4, 8)

    That is an example.
    that would be two lines ... both perpendicular to y = 4x+2 , one passing through (3,-5) and the other passing through (4,8)

    perpendicular slope is the opposite reciprocal of the slope of the given line ... use the point-slope form of a linear equation to find each line's equation.
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    Re: Find equation of a line perpendicular to something passing through something and

    that was just an example, switch 4,8 with 2, -4 then so it's one line

    I'm not comfortable with the pointslope formula but with substituting.
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    MHF Contributor ebaines's Avatar
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    Re: Find equation of a line perpendicular to something passing through something and

    Quote Originally Posted by Ashir View Post
    Find the equation of a line perpendicular to y=4x+2 passing through (3,-5) and (4, 8)

    That is an example.
    This is impossible as written. You can find a line that is perpendicular to y=4x+2 that passes through (3,-5), or you can find a line that is perpendicular to y=4x+2 that passes through (4,8), but there is no single line that is perpendicular to y=4x+2 and that passes through BOTH (3,-5) and (4,8).
    Last edited by ebaines; October 16th 2012 at 12:08 PM.
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    MHF Contributor ebaines's Avatar
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    Re: Find equation of a line perpendicular to something passing through something and

    Quote Originally Posted by Ashir View Post
    that was just an example, switch 4,8 with 2, -4 then so it's one line

    I'm not comfortable with the pointslope formula but with substituting.
    If you are given two points such as (3,-5) and (2, -4) you can find the equation of the line that includes both of these poimts using the formula:

    y=mx+b where m is the slope: m=\frac {\Delta y}{\Delta x} = \frac {(y_2-y_1)}{(x_2-x_1)} and b (the y intercept) can be found from  y_1 = mx_1+b. So here you have y=\frac {-4- (-5)}{2-3} = -1, and -5=(-1)(3) + b, so  b = -5+3 = -2. So the equation of the line passing through these two points is y=-x-2.

    But this has nothing to do with a line being perpendicular to y = 4x+2, because it's not.
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