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My solution and my book's solution don't match.

Is something wrong with the my solution?
If so, where and why?

My book says:

The radius r of a circle increases by 50%.
In terms of r, what is the area of the circle
with the increased radius?

My solution:

  1. A = $\pi r^2\ $ => Area of any circle
  2. ir = $\ 3r/2 \ $ => Increased radio
  3. A$\ _{ir} = \pi ir^{2} \ $ => Area of circle with increased radio
  4. A$\ _{ir} = \pi (3r/2 )^{2} \ $ => Substituting ir with its value
  5. A$\ _{ir} = \pi (9r^2/4 ) \ $ => Square
  6. A$\ _{ir} = \ (9\pi r^2 )/4 \ $ => Result

Is the In terms of r tricky?

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  • 1
    $\begingroup$ What's the solution from your book? $\endgroup$ – draks ... Oct 9 '12 at 14:25
  • $\begingroup$ @draks: thanks for the interest, the book says: $\ (4\pi r^2 )/3 \ $ $\endgroup$ – user454322 Oct 9 '12 at 14:30
  • $\begingroup$ @EmmadKareem: thanks. Not sure what does "Increased ratio" means, that is what the problem says. I am assuming that means 3r/2. $\endgroup$ – user454322 Oct 9 '12 at 14:31
  • 2
    $\begingroup$ your book is wrong... $\endgroup$ – draks ... Oct 9 '12 at 14:32
  • 1
    $\begingroup$ Well.....it took me a while, and I was getting crazy. The truth is that: I was looking at the wrong solution, the book is right...so embarrassed $\endgroup$ – user454322 Oct 12 '12 at 16:19
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There is nothing wrong with your answer!

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