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September 29th, 2012, 04:22 AM   #1
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I have a question about the area of this shape?

Picture 1 and 3 are related to this question; Where did the nr. 15 come from?

Picture 3: How do I figure this out?

I found the area of the circle and then I found the area of the other shape and lastly added the two. (Of course, I was wrong.)
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 Areal 8.PNG (10.1 KB, 86 views) showimage.png (3.8 KB, 86 views)

September 29th, 2012, 04:26 AM   #2
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Re: I have a question about the area of this shape?

Quote:
 Originally Posted by mathismydoom Picture 1 and 3 are related to this question; Where did the nr. 15 come from? Picture 3: How do I figure this out? I found the area of the circle and then I found the area of the other shape and lastly added the two. (Of course. I was wrong.)
I forgot to attach picture 3:
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 2012-09-29 11.48.24.jpg (39.9 KB, 84 views)

 September 29th, 2012, 05:04 AM #3 Global Moderator   Joined: Dec 2006 Posts: 18,586 Thanks: 1489 The triangle is being assumed to be equilateral, so that half its base is 15 cm. That's how the value "15" was obtained. Picture 3 seems to be giving an unrelated shape. I suggest you find the shape's area by adding the area of its rectangular lower portion to the area of its semicircular upper portion. Are you able to do that?
September 29th, 2012, 05:33 AM   #4
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Re:

Quote:
 Originally Posted by skipjack The triangle is being assumed to be equilateral, so that half its base is 15 cm. That's how the value "15" was obtained. Picture 3 seems to be giving an unrelated shape. I suggest you find the shape's area by adding the area of its rectangular lower portion to the area of its semicircular upper portion. Are you able to do that?
I did that and I didn't get the correct answer.

 September 29th, 2012, 05:40 AM #5 Global Moderator   Joined: Dec 2006 Posts: 18,586 Thanks: 1489 If you post your working, we can check it for you.
September 29th, 2012, 06:10 AM   #6
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Re:

Quote:
 Originally Posted by skipjack If you post your working, we can check it for you.
Rectangle: 0.76 * 0.52 = 0.39 m^2

Half circle: 0.0314*0.76 = 0.023

0.39 + 0.023 = 0.413 m^2

The answer is supposed to be 0.62 m^2

 September 29th, 2012, 06:34 AM #7 Senior Member     Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,155 Thanks: 464 Math Focus: Calculus/ODEs Re: I have a question about the area of this shape? For the area of the semi-circle, you want to take half the diameter, then square it and multiply by ?/2: $\frac{\pi}{2}(0.38\text{ m})^2\approx0.23\text{ m^2}$ Recall the area of a circle is $\pi r^2$ Then the total area is about: $(0.39+0.23)\text{ m^2}=0.62\text{ m^2}$

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