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# C4 Differentiation watch

1. Hi.. I have a question from the Edexcel textbook's mixed exercise on differentiation.

The diagram shows part of the curve C with parametric equations: x=t2, y=sin2t, t≥0

The point A is an intersection of C with the x-axis.

a) Find, in terms of pi, the x-coordinate of A.

This seemed simple enough: setting y=0 and so 0=sin2t.. now when this is solved, obviously t can take the value of 0 or pi/2 and so the x-coordinate could be 0 or (pi/2)2.. But given that the question defines t≥0, I don't understand why we can just dismiss the x-coordinate as being where t = 0...

Thanks for any help in advance
2. (Original post by dslc)
But given that the question defines t≥0, I don't understand why we can just dismiss the x-coordinate as being where t = 0...

Thanks for any help in advance
If t=0, then x=y=0, and you have the origin, which is clearly distinct from A. And thus we can dismiss t=0.
3. I presume you make that judgement based on the diagram?

Without that being included, wouldn't t=0 be fair?

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4. (Original post by dslc)
I presume you make that judgement based on the diagram?

Without that being included, wouldn't t=0 be fair?
Yes, bu without the diagram, you wouldn't know what area to look at as there are multiple places where y=0.

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