P=πr², d=2πr
πr²=7
r²=7/π
r=√7/π
d=2π*√7/π=2√7π
[tex]\\\ P= 7 \Pi \\\\ P=\Pi r^2 \\\\ \Pi r^2=7\Pi |:\Pi \\\\ r^2=7 \\\\ r=\sqrt{7} \\\\ l=2 \Pi r\\\\ l=2 \Pi \cdot \sqrt{7} \\\\ l=2 \sqrt{7} \Pi[/tex]
