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# C4 Parametric Equations Question Watch

1. hey!
i seem to be stuck on this question:
http://www.mei.org.uk/files/papers/c408ju_op58.pdf
(paper A, question 5)
I've gotten part a) which is 3u
but im completely stuck on part b)
i have a test tomorrow so would be really grateful!
thanks
2. Use your x or y value to substitute and rearrange to find the value of u at that point

Edit: use both x and y values. Using the x value only will give two possible values of u, you need the y to confirm which is right
3. (Original post by Serine Soul)
Use your x or y value to substitute and rearrange to find the value of u at that point

Edit: use both x and y values. Using the x value only will give two possible values of u, you need the y to confirm which is right
i dont really understand sorry could you show me please? xx
4. (Original post by xoharrypotter)
i dont really understand sorry could you show me please? xx
Right, so you're given the coordinates of the point to be (5,16) so x=5 and y=16 at this point

The first parametric equation states that
x= 1 + u^2

If I sub in x= 5, I can rearrange 5 = 1 + u^2 to find that u is either 2 or -2

u can be either value so we use the equation involving y, setting 16 = 2u^3. From rearranging this, we find that u can only be positive 2 (cube root of a positve number is always positive)

Does that make a bit of sense?
5. (Original post by Serine Soul)
Right, so you're given the coordinates of the point to be (5,16) so x=5 and y=16 at this point

The first parametric equation states that
x= 1 + u^2

If I sub in x= 5, I can rearrange 5 = 1 + u^2 to find that u is either 2 or -2

u can be either value so we use the equation involving y, setting 16 = 2u^3. From rearranging this, we find that u can only be positive 2 (cube root of a positve number is always positive)

Does that make a bit of sense?
yes thank you so much!
thats really helped a lot
sorry im a bit clueless sometimes
thank you again xx

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