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how to work out the area of a circle

i need to know how to work out the area of a circle by using the diameter
so if the diameter was 12.3 what would be the answer and how would you work it out?

Reply 1

James

14

Have you learnt any formulas for finding the area of a circle?

Reply 2

BJack

19

A = \pi r^2

d = 2r

\Rightarrow A = \frac{1}{4}\pi d^2

Reply 3

Louismoore16

OP

right so just let me check ive done this question right and if i have im sorted
the question was find the area of a circle by using diameter=14.8cm
so i do 14.8 divided by 2=7.4 pie time 7.4 squared=172.3

is this correct?

Reply 4

letsdothetimewarpagain

19

3.14*6.15 squared = 118.76 (2dp)

I think

Reply 5

IChem

11

It's 172.03, but I'm guessing that was just a typing error.

Reply 6

L-C-17

Right, this is a rhyme (!) which will mean u never 4get this formulae again!!!

Tweedle dum and tweedle dee,
round the circle is pie x d,
but if the area be declared,
the formula is pie x r squared!

Learn this and then use it. Obviously, d is diameter and r is radius!

Enjoy! :biggrin:

Reply 7

hermaphrodite

15

pie r squared where r is half the diameter

Reply 8

L-C-17

Sounds about right 2 me. Is this work 4 2morrow lol? :p:

Reply 9

username167718

4

Louismoore16

right so just let me check ive done this question right and if i have im sorted
the question was find the area of a circle by using diameter=14.8cm
so i do 14.8 divided by 2=7.4 pie time 7.4 squared=172.3

is this correct?

You've changed the question slightly. In your first post, you said the diameter = 12.3

But anyway, if the diameter is 14.8cm, then the area is 172.0336... (not 172.3), but you'd probably want to round that down to 172cm squared.

Reply 10

Louismoore16

OP

ok thanks for all you help
L-C-17: this is for my maths homework lol
Tomthecool: i changed the question half way throught to 14.8 so i could check if i go it right
and IChem: yes i ment to put 172.03 but my key is abit sticky lol
and sorry about posting so much of the same thing, my page kept refreshing and sending.

how to work out the area of a circle

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