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C4 Edexcel - Coordinate Geometry; help! Watch

1. I've come across a question and i'm really not sure where to start.

Part a) of the question has given me a curve which looks pretty much like this. It has the parametric equations:

x=cost, y=sin2t, 0 <(or equal to) t < 2

I've been asked to find an expression for dy/dx in terms of the parameter t. I have done something (which I need for part b)) but I don't know if it's correct; I got -2cos2tcosect by doing dy/dt x dt/dx.

Part b) is where i'm having problems. It says 'Find the values of the parameter t at the points where dy/dx=0'. I think this is where y=1 and y=-1, but as i've said, i'm having difficulties tackling this question.

I would really appreciate if someone helped me out here.

2. First of all, your answer to part (a) is correct. It is simply an application of the Chain Rule.

For part (b) you have to set the expression that you get in (a) equal to zero, then solve for t. Personally I would draw a graph of the relevant function with the appropriate domain (the inequality that you have quoted). It might also help you to write 2t = theta or some other variable.

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Updated: March 27, 2013
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