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Math Help - slopes

  1. #1
    Geo
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    slopes

    Ok I think I've worked this out incorrectly so if someone could point me in the right direction that would be great.....

    The question is find the equation of a line that passes through (-1,5) and (2,-4)
    I know that
    y=mx+c to find M = change in y value divide by change in x value=

    2- (-1)/5-(-4) = 3/9 =1/3

    so y = 1/3x=c

    so 5=1/3(-1)+c
    5= -1/3+c
    5+-1/3 = c
    4 2/3 = c so
    y= 1/3x+ 14/3

    You see why I need help right?
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  2. #2
    A riddle wrapped in an enigma
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    Quote Originally Posted by Geo View Post
    Ok I think I've worked this out incorrectly so if someone could point me in the right direction that would be great.....

    The question is find the equation of a line that passes through (-1,5) and (2,-4)
    I know that
    y=mx+c to find M = change in y value divide by change in x value=

    2- (-1)/5-(-4) = 3/9 =1/3 Your slope is calculated incorrectly. Look at my slope formula below.

    so y = 1/3x=c

    so 5=1/3(-1)+c
    5= -1/3+c
    5+-1/3 = c
    4 2/3 = c so
    y= 1/3x+ 14/3

    You see why I need help right?

    First find the slope using (-1, 5) and (2, -4):

    m=\frac{y_2-y_1}{x_2-x_1}

    m=\frac{-4-5}{2-(-1)}

    m=\frac{-9}{3}=-3

    Now, use y=mx + b to find the y-intercept (b). We'll use (x, y) = (-1, 5) for our point and m = -3.

    y=mx+b

    5=-3(-1)+b

    2 = b

    Finally, putting it all together with m=-3 and y-int = 2, we have:

    y=-3x+2
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  3. #3
    Geo
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    Right had them round the wrong way. That clears it up. Your a star!!
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