AQA FP3 Polar Co-ordinates Watch

maggiehodgson
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#1
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The question asks to plot r=2sin3theta -pi < theta <= pi. This I've done.

It then asks
"Give the polar equation of the tangents to the curve at the pole".

This is when r = 0 isn't it?

I got theta = -2/3 pi, -1/3 pi, 0, 1/3 pi, 2/3 pi and pi.

However the answers are none on the negative values, the positive ones in my list and also 4/3 pi and 5/3 pi . Aren't these two out of range? And why not my minus answers?
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ghostwalker
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(Original post by maggiehodgson)

I got theta = -2/3 pi, -1/3 pi, 0, 1/3 pi, 2/3 pi and pi.

However the answers are none on the negative values, the positive ones in my list and also 4/3 pi and 5/3 pi . Aren't these two out of range? And why not my minus answers?
If you add 2pi to your negative ones you get their other two positive ones, so you have the same set of answers, in effect.

As to why they're using two "out of range" rather than the two negative ones, I've no idea. I would have said your answer was fine.
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maggiehodgson
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(Original post by ghostwalker)
If you add 2pi to your negative ones you get their other two positive ones, so you have the same set of answers, in effect.

As to why they're using two "out of range" rather than the two negative ones, I've no idea. I would have said your answer was fine.

OK thanks.
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BabyMaths
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(Original post by maggiehodgson)
OK thanks.
It depends on the convention chosen 0-2pi or -pi to pi.

My calculator's Pol(x,y) function gives -\pi&lt;\theta \le \pi.

Edit: I just realised I wrote "\pi." thus infringing Paul Ingrisano's copyright. :eek:
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