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# FP2 polar co-ords understanding question watch

1. June 2013 Q8, here is the paper; http://qualifications.pearson.com/co...e_20130621.pdf page 24 of the pdf

and my working;

what is the significance of the and ?

do they tell you anything about the plot or do you just neglect them by realising the angle required is roughly equal to

(kind of like how in mechanics projectiles when using to find t you sometimes get the minus t value which you usually ignore)
2. dont think it has any real significance in this case, other than that the curve also meets the half line at the origin
3. (Original post by DylanJ42)
do they tell you anything about the plot or do you just neglect them by realising the angle required is roughly equal to
Although it's not obvious from the diagram, gives a point where the tangent is parallel to the initial line, but it's actually the origin. We discard it as the requirement is P is distinct from O.

The other value of theta will also give rise to a line parallel to the initial line, but it's outside the domain of the definition of C, so we can again discard it.
4. (Original post by drandy76)
dont think it has any real significance in this case, other than that the curve also meets the half line at the origin
PRSOM

(Original post by ghostwalker)
Although it's not obvious from the diagram, gives a point where the tangent is parallel to the initial line, but it's actually the origin. We discard it as the requirement is P is distinct from O.

The other value of theta will also give rise to a line parallel to the initial line, but it's outside the domain of the definition of C, so we can again discard it.
i've never realised that the tangent was parallel to initial line at the origin ever, i always thought it was a mysterious recurring solution which we ignored "just because" and i never understood why , but this all makes complete sense now

thank you both
5. If as then is a tangent to the curve.
6. (Original post by B_9710)
If as then is a tangent to the curve.
is this what is happening at the origin?

if i was to zoom in really close...

would be a solution to with that same reasoning
7. (Original post by DylanJ42)
is this what is happening at the origin?

if i was to zoom in really close...

would be a solution to with that same reasoning
yeah, comes up a lot in OCR as a precursor to finding area bound by the curve, since the tangents at the origin can be taken as the limits
8. (Original post by drandy76)
yeah, comes up a lot in OCR as a precursor to finding area bound by the curve, since the tangents at the origin can be taken as the limits
exactly yea you're right, i always know to take limits from 0 to pi/2, so i guess it follows that tangents exist at 0 and pi/2
Spoiler:
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you know when you sometimes feel like you shouldn't be doing further maths.. yeaa now is one of those times
9. (Original post by DylanJ42)
exactly yea you're right, i always know to take limits from 0 to pi/2, so i guess it follows that tangents exist at 0 and pi/2
Spoiler:
Show
you know when you sometimes feel like you shouldn't be doing further maths.. yeaa now is one of those times
Dw about it just probs not covered in your syllabus, for instance I never know what's going on when people mention conics

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10. (Original post by drandy76)
Dw about it just probs not covered in your syllabus, for instance I never know what's going on when people mention conics
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yea i guess, i know it now and that's the main thing thanks again
11. (Original post by drandy76)
Dw about it just probs not covered in your syllabus, for instance I never know what's going on when people mention conics

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