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why is my math wrong?


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kamberkash 
Copper - Posts: 89
Copper spacespace
Joined: March 11, 2007
Location: Kentucky, United States
Posted: November 18, 2007 at 7:09 PM / IP Logged  
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?
the12volt 
Administrator - Posts: 3,955
Administrator spaceThis member has made a donation to the12volt.com. Click here for more info.spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spaceThis member has been recognized as an authority in Mobile Security and Convenience. Click here for more info.spacespace
Joined: March 07, 2002
Location: Louisiana, United States
Posted: November 18, 2007 at 7:28 PM / IP Logged  

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 :)

why is my math wrong? -- posted image. the12volt • Support the12volt.com
i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: November 18, 2007 at 7:31 PM / IP Logged  

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

haemphyst 
Platinum - Posts: 5,054
Platinum spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: November 18, 2007 at 8:12 PM / IP Logged  
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...
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."
kamberkash 
Copper - Posts: 89
Copper spacespace
Joined: March 11, 2007
Location: Kentucky, United States
Posted: November 19, 2007 at 9:44 AM / IP Logged  

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.

haemphyst 
Platinum - Posts: 5,054
Platinum spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: November 19, 2007 at 1:33 PM / IP Logged  
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! why is my math wrong? -- posted image.
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."

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