# FP1 Help

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#1
I got question 9 (d) and (e) incorrect, I've looked at the markscheme but I still don't quite understand the concepts used to work out the center and radius of the circle here. Help?

http://pmt.physicsandmathstutor.com/...%20Edexcel.pdf

Mark Scheme : http://pmt.physicsandmathstutor.com/...%20Edexcel.pdf
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5 years ago
#2
(Original post by togouni2017)
I got question 9 (d) and (e) incorrect, I've looked at the markscheme but I still don't quite understand the concepts used to work out the center and radius of the circle here. Help?

http://pmt.physicsandmathstutor.com/...%20Edexcel.pdf

Mark Scheme : http://pmt.physicsandmathstutor.com/...%20Edexcel.pdf
My FP1 is Rusty but I think I have it figured.

The points opq are on the circle, and you've proved the angle is pi/2.
There is a circle theorem where a triangle in a circle where all three points touch the circle and contains a right angle must have a line across the diameter. Therefore PQ is a diameter and the centre is simply the average of the x's (The real) and the y's (the complex)

for e) pythagoras gives you a distance which must be the radius as it's from the origin (which from the centre is a radius)
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#3
(Original post by plaguarist)
My FP1 is Rusty but I think I have it figured.

The points opq are on the circle, and you've proved the angle is pi/2.
There is a circle theorem where a triangle in a circle where all three points touch the circle and contains a right angle must have a line across the diameter. Therefore PQ is a diameter and the centre is simply the average of the x's (The real) and the y's (the complex)

for e) pythagoras gives you a distance which must be the radius as it's from the origin (which from the centre is a radius)
damn circle theorems! Been a long time since GCSE Maths last gave me a slap in the face.
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