Acircular pool with a diameter of 18 ft will have a uniform 4 ft concrete walkway poured around it. if the concrete cost $4.25 a square foot, how much will it cost for the concrete? a. $1,247.08 b. $1,174.70 c. $1,714.07 d. $276.40

geometry: triangles

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call the larger triangle abc

then the smaller triangle cde is similar to abc (all angles are equal, aaa).  

ab is the side that is 36, and we wish to find de, the side corresponding to ab

area_cde = area_abc - area_cde --> area_abc / area_cde = 2

let x=length of de

ratio of areas = (ratio of sides)^2

+2+=+%2836%2fx%29%5e2+

+2+=+1296%2fx%5e2+

++x%5e2+=+1296%2f2+=+648+

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