Four circles

1) Calculate the circle radius if its area is 400 cm square
2) Calculate the radius of the circle whose circumference is 400 cm.
3) Calculate circle circumference if its area is 400 cm square
4) Calculate the circle's area if perimeter 400 cm.

Result

r1 =  11.284 cm
r2 =  63.662 cm
o1 =  70.899 cm
S2 =  12732.405 cm2

Solution:

S1=400 cm2 r1=S1/π=400/3.1416≐11.2838=11.284  cm S_{ 1 } = 400 \ cm^2 \ \\ r_{ 1 } = \sqrt{ S_{ 1 }/\pi } = \sqrt{ 400/3.1416 } \doteq 11.2838 = 11.284 \ \text{ cm }
o2=400 cm r2=o2/(2π)=400/(2⋅ 3.1416)≐63.662=63.662  cm o_{ 2 } = 400 \ cm \ \\ r_{ 2 } = o_{ 2 }/(2 \pi) = 400/(2 \cdot \ 3.1416) \doteq 63.662 = 63.662 \ \text{ cm }
o1=2π⋅ r1=2⋅ 3.1416⋅ 11.2838≐70.8995=70.899  cm o_{ 1 } = 2 \pi \cdot \ r_{ 1 } = 2 \cdot \ 3.1416 \cdot \ 11.2838 \doteq 70.8995 = 70.899 \ \text{ cm }
S2=π⋅ r22=3.1416⋅ 63.6622≐12732.4046=12732.405 cm2S_{ 2 } = \pi \cdot \ r_{ 2 }^2 = 3.1416 \cdot \ 63.662^2 \doteq 12732.4046 = 12732.405 \ cm^2

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