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    I can't seem to get this question right:
    The co-ordinates are : ( 1/2 , - 1/2 ) and gradient is 5/2

    I substitute the values in the line equation and should get:
    10x - 4y - 7 =0 but I dont :confused:

    -----------------------------

    y + 1/2 = 5/2 ( x - 1/2 )

    Multiply through by 2 from the left to give:
    2y + 1 = 5 ( 2x - 1 )

    I get 5 as 10/2 is 5, and -2/2 is -1 ?

    So 2y+1 = 10x -5
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    (Original post by Gelato)
    I can't seem to get this question right:
    The co-ordinates are : ( 1/2 , - 1/2 ) and gradient is 5/2

    I substitute the values in the line equation and should get:
    10x ? 4y ? 7 =0 but I dont :confused:

    -----------------------------

    y + 1/2 = 5/2 ( x - 1/2 )

    Multiply through by 2 from the left to give:
    2y + 1 = 5 ( 2x - 1 )

    I get 5 as 10/2 is 5, and -2/2 is -1 ?

    So 2y+1 = 10x -5
    youdidnt multiply by the -1/2 as well
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    (Original post by hazbaz)
    youdidnt multiply by the -1/2 as well
    Doesn't that go away if I multiplied it by 2 ? It'll give -1 ?
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    y + 1/2 = 5/2 ( x - 1/2 )

    ^ The line after this should be:

    2y + 1 = 5(x - 1/2)

    What you did was multiply the RHS by 4.
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    You need to realise that if you expand [ 5/2 ( 2x - 1) ] , you get TWO terms and not THREE terms.You have multiplied 2 with all three numbers whereas infact there are two [ 5x/2 and 5/4]

    Simple.Expand the brackets-

    y + 0.5 = 2.5 ( x - 0.5 )

    y + 0.5 = 2.5x - 1.25

    2.5x - y = 0.5 + 1.25

    2.5x - y = 1.75

    Multiply throughout by 4.
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    (Original post by electriic_ink)
    y + 1/2 = 5/2 ( x - 1/2 )

    ^ The line after this should be:

    2y + 1 = 5(x - 1/2)

    What you did was multiply the RHS by 4.
    Oh so when I multiply the rhs by 2, only the stuff outside the bracket gets multiplied ?
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    (Original post by Gelato)
    Oh so when I multiply the rhs by 2, only the stuff outside the bracket gets multiplied ?
    Yes (or you could multiply the stuff inside the bracket). I suppose the best way to explain it is to multiply out the bracket:

    (\frac{5}{2}(x - \frac{1}{2})) \times 2
    = (\frac{5}{2}x - \frac{5}{4}) \times 2
    = 5x - \frac{5}{2}
    = 5 ( x - \frac{1}{2} ) (the same as multiplying what's outside the bracket).
    = \frac{5}{2} ( 2x - 1 ) (the same as multiplying what's inside the bracket).
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    y1 = -\frac{1}{2}

    x1 = \frac{1}{2}

    m = \frac{5}{2}

    You use

    y - y1 = m(x - x1)

    Substitute the values in to get:

    y - -\frac{1}{2} =  \frac{5}{2}(x-\frac{1}{2})

    The left side can be converted to a sum as a negative and a negative make a positive:

    y + \frac{1}{2} =  \frac{5}{2}(x-\frac{1}{2})

    When you multiply out the right hand side you get:

    y + \frac{1}{2} =  \frac{5}{2}x -\frac{5}{4}

    Take \frac{1}{2} off both sides:

    y =  \frac{5}{2}x -\frac{7}{4}

    Now get rid of the fractions, so multiply everything by 2:

    2y =  5x -\frac{7}{2}

    And then again multiply by 2:

    4y =  10x - 7

    Then put everything on one side:

    10x - 4y - 7 = 0


    The only reason I went through it so many steps is for you to understand how to do it, I know I shouldn't really be showing you how to do it straight away but it looks like the other guys have already helped you out enough for me to show you how I would do it. Also, when I was getting rid of the fractions, I understand I couldn't multiplied everything by 4 straight off the bat, however I wanted to show you exactly the steps that were taking place to make it easier.


    Hope that helped =D
 
 
 
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