why is my math wrong?

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Forum Name: Car Audio
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URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=99132
Printed Date: May 14, 2025 at 7:37 PM

Topic: why is my math wrong?

Posted By: kamberkash
Subject: why is my math wrong?
Date Posted: November 18, 2007 at 7:09 PM

im trying to convert a 40 in^2 port in to a circle.

Area=3.14(r^2)   (for a circle)

ok....

40    =   3.14(r^2)
-3.14      -3.14
            _________________________
36.86 = r^2

the square root of 36.86 is 6.07.

so .i plug this number in as the radius

A=3.14(6.07^2)

solve for A and i keep getting 115.69

A is supposed to be 40!
What little aspect am i forgetting?

Replies:

Posted By: the12volt
Date Posted: November 18, 2007 at 7:28 PM

Divide both sides by 3.14 instead of subtracting 3.14 from both sides.

40 = 3.14(r^2)
40/3.14 = r^2
12.74 = r^2
3.569 = r

40 = 3.14(3.569^2)
40 = 3.14(12.74)
40 = 40 :)

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Posted By: i am an idiot
Date Posted: November 18, 2007 at 7:31 PM

The area of a 7 inch circle is 38.48 square inches. 7.25 inch circle = 41.28 7-1/8 inch circle = 39.8711

Hope this helps

Posted By: haemphyst
Date Posted: November 18, 2007 at 8:12 PM

Area divided by pi, and the square root of that provides your radius...

40/3.141592=12.74

sqrt12.74=3.5

Work it backwards to check my math...

3.5*3.5=12.75*3.141592= about 40

You're looking for a 7 inch port...

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Posted By: kamberkash
Date Posted: November 19, 2007 at 9:44 AM

DUH! Im supposed to DIVIDE! i racked my brain last night trying to figure out what i was missing. Thats a result of too much caffeine, with not enough sleep! Thanks guys.

Posted By: haemphyst
Date Posted: November 19, 2007 at 1:33 PM

kamberkash wrote:

DUH! Im supposed to DIVIDE! i racked my brain last night trying to figure out what i was missing. Thats a result of too much caffeine, with not enough sleep! Thanks guys.

There'snevertoomuchcaffeine!Andsleepisover-rated! posted_image

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."