How to Find the Centre of a Circle

The POSH way

Draw a chord anywhere across your circle (marked in yellow on the picture)
Construct the perpendicular bisector (marked in blue on the picture).
Draw another chord and do the same thing.
Where the bisectors cross will be the centre.

The USING A BOOK way

1/ Get a circle 2/ Get a book that's at least as big as the circle. (If you haven't got a book you can use a rectanglular piece of paper). 3/ Put one corner of the book on the edge of the circle (See "C") Mark where the two edges of the book cross the circle (See "X" and "X")

4/ Remove the book and join the marks with a straight line. This will be a diameter of the circle 5/ Do it again to get another diameter. 6/ Where the diameters cross is the centre.

This works thanks to the fact that the angle in a semi-circle is always a right angle. There's more of this stuff in Savage Shapes
You might also like How to find the centre and foci of an ELLIPSE!

How to Find the Centre of a Circle

The POSH way

Draw a chord anywhere across your circle (marked in yellow on the picture) Construct the perpendicular bisector (marked in blue on the picture). Draw another chord and do the same thing. Where the bisectors cross will be the centre.

The USING A BOOK way

This works thanks to the fact that the angle in a semi-circle is always a right angle. There's more of this stuff in Savage Shapes You might also like How to find the centre and foci of an ELLIPSE!

To the RESEARCH LAB Murderous Maths Main Index Page

Draw a chord anywhere across your circle (marked in yellow on the picture)
Construct the perpendicular bisector (marked in blue on the picture).
Draw another chord and do the same thing.
Where the bisectors cross will be the centre.

This works thanks to the fact that the angle in a semi-circle is always a right angle. There's more of this stuff in Savage Shapes
You might also like How to find the centre and foci of an ELLIPSE!

To the RESEARCH LAB
Murderous Maths Main Index Page