Question 1134852
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r = 5 


A = pi * r^2


A = pi * 25 = 3.14159*25 = 78.53975 cm^2 (approximately),  or  78.5 cm^2 rounded to the nearest tenth.



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Regarding the answer by @t0hierry, I assume that a physicist with a PhD degree could make his calculations in a more accurate manner . . .