Decades: 1160s 1170s 1180s 1190s 1200s - 1210s - 1220s 1230s 1240s 1250s 1260s
Years: 1211 1212 1213 1214 1215 - 1216 - 1217 1218 1219 1220 1221
Births
Deaths
... The formula reads <math> x=\frac{-b \pm \sqrt {b^2-4ac}}{2a} </math> The term b2 – 4ac is called the discriminant of the quadratic equation, ...