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Intr-un cerc aria = 81 , aflati lungimea cerc .
Scrieti toata rezolvarea .


Răspuns :

A=πR²
A= 81*π
R²=81
R=9
P= 2πR
P=2*9*π
P=18π
Aria=πr²=81 =>r²=81/π =>r=9√π/π 
Considerand π=3,1415 =>r≈5
Lungimea=2πr=10π=31,415