Rozwiązanie:
T=21s
g≈10s²
[tex]T=2\pi \sqrt{\frac{l}{g} } |:2\pi \\\\\sqrt{\frac{l}{g} } =\frac{T}{2\pi } \\\\\frac{l}{g}=\frac{T^{2} }{(2\pi )^{2} } |*g\\\\l=\frac{T^{2} }{4\pi ^{2} }*g \\\\l=\frac{(21s)^{2} }{4*(3,14)^{2} } *10m/s^{2} \\\\l=\frac{441s^{2} }{39,4} *10m/s^{2} \\\\[/tex]
l≈111,93m
