[tex]Dane:\\l = 90 \ cm = 0,9 \ m\\g = 10\frac{m}{s^{2}}\\\pi = 3\\Szukane:\\f = ?\\\\Rozwiazanie\\\\T = 2\pi \sqrt{\frac{l}{g}} = 2\cdot3\cdo\sqrt{\frac{0,9 \ m}{10\frac{m}{s^{2}}}} = 6\cdot\sqrt{0,09 \ s^{2}} = 6\cdot0,3 \ s = 1,8 \ s\\\\\\\underline{f = \frac{1}{T}}\\\\f = \frac{1}{1,8 \ s}\\\\\boxed{f = 0,(5) \ Hz \approx0,56 \ Hz}[/tex]
