Definition
Diameter
A diameter crosses a circle through its centre and has length equal to two radii.
Continue from this idea into connected AXIO math.
What it means
Draw a straight line from one side of a circle to the other through the exact centre. That whole across-the-centre segment is a diameter. It is two radii placed end to end.
Remember it
Edge to centre to edge: radius + radius = diameter.
Example
A circle has radius 4.5 cm. Its diameter is 2 × 4.5 cm = 9 cm.
Watch for
A chord that joins two points on the circle but misses the centre is not a diameter.
Common mix-up
Radius goes from centre to edge; diameter goes edge to edge through the centre.
Exact meaning
A diameter of a circle is a line segment whose endpoints lie on the circle and which passes through the centre. Diameter also names that segment’s length, equal to twice the radius.