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# FP1

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1. 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
2. (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.
3. (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
4. (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.
5. (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
6. (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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