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Math Help - coordinate geometry

  1. #1
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    coordinate geometry

    The vertices of the triangle ABC have coordinates A(-5,3) , B(-2,0) and
    C(4,-1) . Find the equations of the sides of the triangle.
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  2. #2
    Like a stone-audioslave ADARSH's Avatar
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    The equation of line joining two points
    (a,b) and (c,d) is given by

    (y -b) = \frac{(d-b)}{(c-a)} \times{(x-a)}


    You have three points and you are asked to find the equations of those three lines which join them
    Now think ahead yourself and tell if you feel trouble
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  3. #3
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    Quote Originally Posted by ADARSH View Post
    The equation of line joining two points
    (a,b) and (c,d) is given by

    (y -b) = \frac{(d-b)}{(c-a)} \times{(x-a)}


    You have three points and you are asked to find the equations of those three lines which join them
    Now think ahead yourself and tell if you feel trouble

    I have not come across this equation, my book tells me to use this equation.

     \frac{y-y_1}{y_2-y_1} =\frac{x-x_1}{x_2-x_1} but I have got three points, so am not sure how to work it out.
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  4. #4
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    Quote Originally Posted by Tweety View Post
    I have not come across this equation, my book tells me to use this equation.

     \frac{y-y_1}{y_2-y_1} =\frac{x-x_1}{x_2-x_1} but I have got three points, so am not sure how to work it out.
    The equation is the same, if you set (a,\;b)=(x_1,\;y_1), (c,\;d)=(x_2,\;y_2), and divide by y_2 - y_1.

    You have three lines, so you will need to apply the equation three times. Just substitute the coordinates for each pair of points.
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  5. #5
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    Make a sketch on the coordinate plane will make things easier .

    Let me start you off with the line AB .

    The gradient is -1 and we know the line passes through point (-5,3) or
    (-2,0)

    y-y1=m(x-x1)
    thus , y=-x-2

    do it this way for the remaining two sides of the triangle .
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