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    Why is the equation of the tangent passing through X and P (from part a) not the same as the line passing through X and P
    3F Question 10d equation of XP
    https://644625398389466aee0063322305...0NRNU0/CH3.pdf
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    (Original post by Acrux)
    Why is the equation of the tangent passing through X and P (from part a) not the same as the line passing through X and P
    3F Question 10d equation of XP
    https://644625398389466aee0063322305...0NRNU0/CH3.pdf
    They are the same - just using different parameters.

    We have a=ct, so t=a/c. Substitute that into the first equation for the tangent, and you end up with the second equation.

    Method used in the markscheme is a bit round the houses, IMO.
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    (Original post by ghostwalker)
    They are the same - just using different parameters.

    We have a=ct, so t=a/c. Substitute that into the first equation for the tangent, and you end up with the second equation.

    Method used in the markscheme is a bit round the houses, IMO.
    wait so what do i do?
    put a/c in tangent x+t^2y=2ct
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    (Original post by Acrux)
    wait so what do i do?
    put a/c in tangent x+t^2y=2ct
    Yep. Just substitute a/c for t in that equation, and you'll get their second equation.
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    (Original post by ghostwalker)
    Yep. Just substitute a/c for t in that equation, and you'll get their second equation.
    I got ya^2=2a-c^2x
    rearragned to get

    Actually y=-c^2x/a^2 + 2c^2/a
    is this correct ghostwalker
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    (Original post by Acrux)
    I got ya^2=2a-c^2x
    rearragned to get

    Actually y=-c^2x/a^2 + 2c^2/a
    is this correct ghostwalker
    Take out the factor as per the markscheme, and you can see for yourself.
 
 
 
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