[tex]look\ at\ the\ picture\\\\(2r)^2=3^2+4^2\\\\4r^2=9+16\\\\4r^2=25\ \ \ /:4\\\\r^2=\frac{25}{4}\\\\r=\sqrt\frac{25}{4}\\\\r=\frac{\sqrt{25}}{\sqrt4}\\\\r=\frac{5}{2}\\\\circumference\ of\ the\ circle:\\\\L=2\pi r;\ L=2\pi\cdot\frac{5}{2}=5\pi[/tex]
