Find the perimeter of this semi-circle with radius, r = 25cm. Give your answer as an expression in terms of π .

perimeter of circle

2πr

perimeter of semi circle

2πr ÷ 2

=2π(25) ÷ 2

= 50π ÷ 2

= 25π

Ans = 25π

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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