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Math Help - Straight Lines

  1. #1
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    Straight Lines

    Hi there,

    I'm having a little bit of a problem with a simple question, that I know the answer to, but don't know the working to get the answer.

    The question is as follows:

    A(-2, 2) and C(3, -1) are opposite vertices of kite ABCD. Find the gradient of diagonal BD.

    I know the answer is 5/3 but I don't know *how* that is the answer.
    If someone could possibly tell me the formula, it would put my mind at rest.

    Thanks!
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  2. #2
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    Quote Originally Posted by Mathy View Post
    ...

    The question is as follows:

    A(-2, 2) and C(3, -1) are opposite vertices of kite ABCD. Find the gradient of diagonal BD.
    ...
    Hello,

    you are supposed to know that in a kite the diagonals are perpendicular to each other. Therefore

    1. calculate the slope (=gradient) between A and B
    2. calculate the perpendicular slope. That must be the slope between BD

    m=\frac{2-(-1)}{-2-3}=-\frac{3}{5}

    The perpendicular slope is the negative reziprocal value of m. Thus m'=\frac{5}{3}
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  3. #3
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    Yay!

    Thank you. This was my original thought, but I thought that the it may have needed more.

    I'm all happy now.
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