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# Coordinate geometry C4 help watch

1. A curve has parametric equations

C) Find the Cartesian equation of the curve

how would one do this?
2. Just get y in terms of x.

3x = 12Sint

4y = 12Sint
3. (Original post by StephenP91)
Just get y in terms of x.
how do you do that
4. (Original post by ajayhp)
how do you do that
Are they both meant to be sines, rather than one cosine and one sine? If they're both sines, you can write both equations in the form , so you can just equate the two.

If one is a cosine and one is a sine, then write one equation in the form and the other in the form , and then note that (so you can square and add the two "somethings" to eliminate the t terms).
5. (Original post by nuodai)
Are they both meant to be sines, rather than one cosine and one sine? If they're both sines, you can write both equations in the form , so you can just equate the two.

If one is a cosine and one is a sine, then write one equation in the form and the other in the form , and then note that (so you can square and add the two &quot;somethings&quot; to eliminate the t terms).
could you please explain this pls, i don't get what you said

made a mistake changed it
6. (Original post by ajayhp)
could you please explain this pls, i don't get what you said
You have one equation in terms of and one equation in terms of , so you can make and the subjects of the respective equations. Then you can square both sides of the equations so that you have something in the form:

If, then, you add the two equations together, then the LHS will be 1 and the RHS will be something involving x and y... and then you're done.
7. dw i have got the answer
8. If you have parametric equations with trig functions involved, it's useful to have a trig identity so you can substitute x and y in

as nuodai said, cos^2t + sin^2t = 1, how do you get cos t in terms of x ? and how do you get sin t in terms of y ? In other words, substitute for cos t and sin t in terms of x and y and you'll have converted parametric to cartesian equations.

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