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# How to find the centre of rotation?

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1. This is probably a really stupid question, but how do you find the centre of rotation when given a question about shape transformations?
Our school has never said anything about providing us with tracing paper in the exam or anything but it seems to me that the only way I could probably do it is by randomly picking points and then testing it out with the tracing paper?
Or is there a more logical way?
2. Edit: Centre of rotation depends on level. Edit as I read this as Centre of gravity at first.

Draw lines from A to A', B to B' etc. The COR is the intersection of the perpendicular bisectors of those lines.

Another edit: I assume you know how to draw the perpendicular bisector of a line.
3. (Original post by nerak99)
Edit: Centre of rotation depends on level. Edit as I read this as Centre of gravity at first.

Draw lines from A to A', B to B' etc. The COR is the intersection of the perpendicular bisectors of those lines.

Another edit: I assume you know how to draw the perpendicular bisector of a line.
thank you so much! This is for GCSE
4. (Original post by surina16)
This is probably a really stupid question, but how do you find the centre of rotation when given a question about shape transformations?
Our school has never said anything about providing us with tracing paper in the exam or anything but it seems to me that the only way I could probably do it is by randomly picking points and then testing it out with the tracing paper?
Or is there a more logical way?
You'll get tracing paper don't worry, just trace the shape and put your pen on different points and see where you need to put it so that it exactly traces onto the other shape. You'll be able to tell how close you are it is quite quick, then you just state rotation by however many degrees, this is the simplest way.
5. (Original post by _Xenon_)
You'll get tracing paper don't worry, just trace the shape and put your pen on different points and see where you need to put it so that it exactly traces onto the other shape. You'll be able to tell how close you are it is quite quick, then you just state rotation by however many degrees, this is the simplest way.
Really? Trial and improve over two lines and short work with a compass? Obviously you would have to be one of those rare students who brings a ruler to the exam and uses it.
6. (Original post by nerak99)
Really? Trial and improve over two lines and short work with a compass? Obviously you would have to be one of those rare students who brings a ruler to the exam and uses it.
why what's wrong with that??
7. Nothing wrong with it but I am surprised that you could manage to do trial and improve more quickly that construction. Also, depending on the syllabus, you might need to show the construction to get full marks.

Sorry if I appeared overly critical ;-)

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