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Math Help - altitude vertex A in coordinates

  1. #1
    Tuesday's Gone
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    altitude vertex A in coordinates

    Okay so I have to find the length of an altitude from vertex A of triangle ABC

    Co-ordinates: A(3,4) B (4,-3) C (-4,-1)

    Slope of CB= -1/4
    Slope of Altitude= 4

    Equations of the lines: CB y=-1/4x-2
    Altitude A y=4x-8

    Okay I think this is where I go wrong. I am suppose to find the length of the altitude from vertex A so I assume I must find the P.O.I. My answers for that are formed from using substitution:

    x= 24/17 y=-40/17

    Now to find the distance I use length= Squere Root((X2-X1)^2+(Y2-Y1)^2)

    The answer in my book says 6.55 units while I get approx. 9.12 units.

    My question where I am I going wrong? (or is the book wrong...its known for being wrong )
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  2. #2
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    Hello, Tuesday's Gone!

    Your work is correct ... up to finding the length.

    You found that the foot of the altitude is: .D:(24/17, -40/17) . Right!


    The answer in my book says 6.55 units while I get approx. 9.12 units.
    Sorry, the book is right.

    The distance from D:(24/17,-40/17) to A:(3,4) is:
    . . . . . . . . _______________________
    . . d . = . √(3 - 24/17) + (4 + 40/17) . = . 6.548461876 . . 6.55

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