[tex]\bf 7.\\ \\ \it \mathcal{A}_{disc}=\pi R^2=\pi\cdot12^2=144\pi\ cm^2\\ \\ L_{cerc}=2\pi R=2\pi\cdot12=24\pi\ cm[/tex]
8.
[tex]\it \mathcal{A}_{disc}=\pi R^2 \Rightarrow R^2=\dfrac{\mathcal{A}}{\pi}=\dfrac{81\pi}{\pi}=81=9^2 \Rightarrow R=9\ cm\\ \\ L_{cerc}=2\pi R=2\pi\cdot9=18\pi\ cm[/tex]
9.
[tex]\it L_{arc}=\dfrac{2\pi R\cdot45^o}{360^o}=\dfrac{2\pi\cdot6\cdot45^o}{360^o}=\dfrac{540^o^{(180^o}}{360^o}\pi=\dfrac{3}{2}\pi\ cm[/tex]
