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September 22, 2014

September 22, 2014

Posted by **Anonymous** on Thursday, April 4, 2013 at 12:52am.

- calc -
**Reiny**, Thursday, April 4, 2013 at 8:27amLet the width of the rectangle be 2x , making the radius of the semicircle = x

let the height of the rectangle be y

then 2x + 2y + 2πx = 24

x + y + πx = 12

y = 12-x-πx

Assume that the amount of light (L) is a function of the area

L= area of rectangle + (1/2) area of semicircle

= 2xy + (1/2)(1/2)π x^2

= 2x(12-x-πx) + (1/4)π x^2 = 24x - 2x^2 - 2πx^2 + (1/4)π x^2

dL/dx = 24 - 4x - 4πx + (1/2)πx

= 0 for a max of L

times 2

48 - 8x - 8πx + πx = 0

48 = x(8 + 8π - π)

x = 48/(8+7π) = appr1.6

then r = 5.37

State the conclusion

(check my arithmetic, I should have written it out on paper)

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