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Very difficult parametric question ??

for A i tried to work out solution for t by equaling f'(x) to 2 and I got (t^2-9) difference of two squares t= +/- 3 now I can't seem to work from here as I don't think this is the correct solution
plsss
help ??

don't know how to do part c (ii)
(edited 4 years ago)
Original post by Orss_
for A i tried to work out solution for t by equaling f'(x) to 2 and I got (t^2-9) difference of two squares t= +/- 3 now I can't seem to work from here as I don't think this is the correct solution
plsss
help ??
Attachment not found


Why don't you think those values of t are correct?
Well, that's what I just got, too, so why not just substitute those values back into the values for x and y?
Reply 3
Original post by KAF128___
Well, that's what I just got, too, so why not just substitute those values back into the values for x and y?

Got part A how do I continue ??
Reply 4
Original post by ghostwalker
Why don't you think those values of t are correct?

I just wanted to double check my answer :P
Original post by Orss_
Got part A how do I continue ??


You know what x,y are in terms of t.

And the question asks for what x^2, y^2 are in terms of t.

So... naturally, you square the equations.
Reply 6
Original post by Orss_
for A i tried to work out solution for t by equaling f'(x) to 2 and I got (t^2-9) difference of two squares t= +/- 3 now I can't seem to work from here as I don't think this is the correct solution
plsss
help ??
Attachment not found

Screenshot 2020-03-28 at 22.36.56.pngthis is the solution to b - i don't knwo how to solve for t :s-smilie:
Original post by Orss_
Screenshot 2020-03-28 at 22.36.56.pngthis is the solution to b - i don't knwo how to solve for t :s-smilie:

do what it tells you to do and the answer should be clear, you are over-complicating it (but you've solved it anyway wht the left equation is the answer)
Original post by Orss_
Screenshot 2020-03-28 at 22.36.56.pngthis is the solution to b - i don't knwo how to solve for t :s-smilie:


The cartesian equation cannot be expressed in the explicit form "y=..." since there are either 0,1, or 2 possible values for y for a given x value. You need to leave it in implicit form.
b) is just to substitute for x^2; write it in terms of t (repeat for y).
Reply 10
Original post by ghostwalker
The cartesian equation cannot be expressed in the explicit form "y=..." since there are either 0,1, or 2 possible values for y for a given x value. You need to leave it in implicit form.

Ahhh ok x^2-y^2=12

thank you :smile:
Reply 11
Original post by KAF128___
b) is just to substitute for x^2; write it in terms of t (repeat for y).

IMG_3257.jpg
my attempt at part C don't know how to do ii
Original post by Orss_

my attempt at part C don't know how to do ii


I'm just going to assume you did all this correctly since I don't have time to check your working.

For part c(ii) you seek the second point of intersection between the normal, which is the line y+2=12(x4)y+2 = \dfrac{1}{2}(x-4), and the original curve which is defined parametrically.

If both equations were Cartesian, I am sure you would know how to proceed and find points of intersection. The whole 'sub y from one equation into the other and solve for x' type of thing.

But since one eqn is Parametric, and the other is Cartesian, you still aim to end up solving a single equation in one variable.

Your Cartesian line has x,y in there but these can both be expressed in terms of the parameter t.

Hence, if you sub in the curve's defining x,y coordinates in terms of t into the normal line equation, you end up with one equation in t to solve.

If you got the correct normal, then t=1 is obviously one solution corresponding to the point of intersection where you constructed the normal.

You seek *different* solution for t, and once you have it you can sub it back into the curve's eqn to obtain the x,y coordinates.
Reply 13
Original post by RDKGames
I'm just going to assume you did all this correctly since I don't have time to check your working.

For part c(ii) you seek the second point of intersection between the normal, which is the line y+2=12(x4)y+2 = \dfrac{1}{2}(x-4), and the original curve which is defined parametrically.

If both equations were Cartesian, I am sure you would know how to proceed and find points of intersection. The whole 'sub y from one equation into the other and solve for x' type of thing.

But since one eqn is Parametric, and the other is Cartesian, you still aim to end up solving a single equation in one variable.

Your Cartesian line has x,y in there but these can both be expressed in terms of the parameter t.

Hence, if you sub in the curve's defining x,y coordinates in terms of t into the normal line equation, you end up with one equation in t to solve.

If you got the correct normal, then t=1 is obviously one solution corresponding to the point of intersection where you constructed the normal.

You seek *different* solution for t, and once you have it you can sub it back into the curve's eqn to obtain the x,y coordinates.

thank you for your reply
subbed into normal eq I got t^2-9 = 0 which means that t= -3 or t= 3 which is the values I got for t in the beginning part of the question and subbing these into eq for x and y will give me the same coordinates super confused ?? :s-smilie:
Original post by Orss_
thank you for your reply
subbed into normal eq I got t^2-9 = 0 which means that t= -3 or t= 3 which is the values I got for t in the beginning part of the question and subbing these into eq for x and y will give me the same coordinates super confused ?? :s-smilie:


You made algebraic mistakes if you somehow arrived at t29=0t^2 - 9 = 0.

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