Decades: 1180s 1190s 1200s 1210s 1220s - 1230s - 1240s 1250s 1260s 1270s 1280s
Years: 1227 1228 1229 1230 1231 - 1232 - 1233 1234 1235 1236 1237
Deaths
Events
... square; it is the square of (x + b/(2a)). The right side can be written as a single fraction; the common denominator is 4a2. W ...