# Circle's Diameter

• Jan 17th 2007, 04:53 PM
symmetry
Circle's Diameter
If the circumference of a circle is doubled, the diameter of the circle

(1) remains the same
(2) increases by 2
(3) is multiplied by 4
(4) is doubled
• Jan 17th 2007, 05:20 PM
ThePerfectHacker
Quote:

Originally Posted by symmetry
If the circumference of a circle is doubled, the diameter of the circle

(1) remains the same
(2) increases by 2
(3) is multiplied by 4
(4) is doubled

Is doubled.

$C=\pi d$
Thus,
$2C=\pi (2d)$
• Jan 17th 2007, 06:20 PM
symmetry
ok
If the circumference of a circle is 12, the the diameter = pi(12)(d), right?

What whatever the circumference equals, the diameter increases by the same amount, right?
• Jan 17th 2007, 07:05 PM
ThePerfectHacker
Quote:

Originally Posted by symmetry
If the circumference of a circle is 12, the the diameter = pi(12)(d), right?

What whatever the circumference equals, the diameter increases by the same amount, right?

Right
• Jan 18th 2007, 12:52 AM
earboth
Quote:

Originally Posted by symmetry
If the circumference of a circle is 12, the the diameter = pi(12)(d), right?...

Hello,

you know already that the circumference of a circle is calculated by:

$c=2 \cdot \pi \cdot r= \pi \cdot d$, with diameter = 2 * radius.

Plug in the value you know:

$12= \pi \cdot d \Longleftrightarrow d=\frac{12}{\pi}$.

In general:

$c=\pi \cdot d \Longrightarrow d=\frac{12}{\pi} \Longrightarrow \pi=\frac{c}{d}$

EB

PS: I've attached a diagram which helps to memorize the right formula: Cover the variable you want to calculate with your fingertip. The remaining term shows how to calculate the covered value.
• Jan 18th 2007, 12:57 PM
symmetry
ok
Thank you for the notes and reply.

Earboth,

Thank you for the picture. I think tutors should use pictures here to help students.