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06162008  #1 
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Word Problem
I am having some trouble with this problem. I know the answer is 7.
This is the problem... The radius of a large pizza is 1in. less then twice the radius of a small pizza.The difference between the areas of the pizzas is 33pi in^2.Find the radius of the large pizza. So this must be a quadratic equation. This is the part I don't get. Should it be like this... 33pi in^2 + 2r 1=0 Sorry couldn't find the symbol for pie. But would I multiply the 33 first? Or is my formula completely wrong. Or maybe putting the 33 on 2 sets of formulas. One that represents the small and one the large? Then subtracting the difference? Just need a shove in the right direction. Last edited by Equality; 06162008 at 09:12 PM.. Reason: Another Thought 
06162008  #2 
Join Date: Oct 2006
Posts: 822

Well, let the radius of the smaller circle be r, so the radius of the larger circle is 2r1. We then have , since we just divided out the pi. Now, I just eyed it out and found r=4, so our answer is 7. If you can't see that, you can expand to get , so we know r must be 4.
Or, after getting , you can apply difference of squares to get and you can either make it a quadratic again, or in this case it's easy to examine factors and find r=4.
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06172008  #3 
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Ok. Thanks.You gave me more help then I wanted, but I was doing it backwards. So, if I originally left the 33pi^2 on the right and then divided out the square then I would of had the (2r1)^2? This is where that square came from? Something like using a literal equation?We just started quadratic equations and this was the last question in my homework. Thanks a lot for your help, it is appreciated!

06172008  #4 
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One more thing is the r^2 also the result of dividing out the PI?

06172008  #5 
Join Date: Oct 2006
Posts: 822

Well, since we let the radius of the smaller circle be r so the bigger one is 2r1, we can convert what it says to an equation: Since the difference of the areas is 33 pi, we have , so we can divide out pi.
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06172008  #6 
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Thanks...thats what I was looking for.

09212008  #7 
Join Date: Nov 2006
Posts: 446

how do you know the answer?
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