Decades: 1170s 1180s 1190s 1200s 1210s - 1220s - 1230s 1240s 1250s 1260s 1270s
Years: 1215 1216 1217 1218 1219 - 1220 - 1221 1222 1223 1224 1225
Births
Deaths
... a, b and c are complex numbers, or more generally members of any field whose characteristic is not 2. (In a field of characteristic 2, the element 2a is zero and it ...