Equilateral triangle vs circle

Find the area of an equilateral triangle inscribed in a circle of radius r = 9 cm. What percentage of the circle area does it occupy?

Correct result:

S =  105.2221 cm2
p =  41.3497 %

Solution:

r=9 cm  a=3/3⋅ r=3/3⋅ 9=9 3 cm≐15.5885 cm  S=34⋅ a2=34⋅ 15.58852=105.2221 cm2
S1=π⋅ r2=3.1416⋅ 92≐254.469 cm2  p=100⋅ SS1=100⋅ 105.2221254.469=41.3497%

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Pythagorean theorem is the base for the right triangle calculator.
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