[tex]\displaystyle\\\text{Se da:}\\ D = 12~cm~~\text{(Diametrul cercului)}\\\\\text{Se cere:}\\\\ L = ?~cm~~\text{(Lungimea cercului)}\\\\\text{Formule folosite:}\\\\\text{Formula 1: }\\\\L = \pi D=\pi \times 12=\boxed{12\pi~cm} \\\\\text{Formula 2: }\\\\L=2\pi R~~~~\text{unde R este raza cercului.}\\\\R=\frac{D}{2}=\frac{12}{2}=6~cm\\\\L=2\pi R=2\pi \times6=\boxed{12\pi~cm}[/tex]
