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Math Help - slope point equation

  1. #1
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    slope point equation

    This should be easy. This is first time I'm doing these in over a decade.
    Write the equation of the line that goes through point P and has slope m.
    P(-5,2), m = -1

    Here is what I did:

    Y y1 = m( x x1)
    Y 2 = -1(x (-5))
    Y 2 = -x + 5
    Y = -x + 7
    X + y = 7
    Here is what the answer is supposed to be:
    x + y = -3

    how did I screw this up? Thank you.
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  2. #2
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    There's a mistake going from line 2 to 3 on the right-hand side. The x - (-5) becomes x + 5, but when you distribute the -1, you get -x - 5.

    I find that there's an easier way to do these sorts of problems:

    We know the slope is -1 so let's pretend the equation of the line is y = -x. We want it to run through (-5, 2), so we plug in -5 for x. y = 5 then. So we are 3 units above our goal, which is 2. So we need to come down 3. Thus, the equation is actually y = -x - 3.
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  3. #3
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    EDIT: nevermind
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  4. #4
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    Thanks for the help
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