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.

Correct answer:

r1 =  11.2838 cm
r2 =  63.662 cm
o1 =  70.8982 cm
S2 =  12732.3954 cm2

Step-by-step explanation:

S1=400 cm2 r1=S1/π=400/3.1416=11.2838 cm
o2=400 cm r2=o2/(2π)=400/(2 3.1416)=63.662 cm
o1=2π r1=2 3.1416 11.2838=70.8982 cm
S2=π r22=3.1416 63.6622=12732.3954 cm2=1.273104 cm2

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