Question

Un cerc are aria 4 π cm².Afla lungimea cercului.

Answer 1

A= π r²
A= 4 π cm²
⇒r²= 4 ⇒ r ²= 2² ⇒r=2

L = 2 π r = 2· π ·2= 4 π cm

Answer 2

$A_{cerc}= 4 \pi ~cm^2 \\ \pi r^2=4 \pi \\ r^2=4 \pi : \pi \\ r^2=4 \\ r= \sqrt{4} \\ r=2 \\ L=2 \pi r=2 \pi \cdot2=4 \pi ~cm$