Zamień na ułamek zwykły
2,(21)
x = 1,(21)… /*100 100x = 121,(21)… 100x - x = 121,(21) - 1,(21) 99x = 120 /:99 x = 120/99
x=2,21.../*100
100x=221,21...
100x-x=221,21...-2,21..
99x=219
x=\frac{219}{99}