Decades: 1220s 1230s 1240s 1250s 1260s - 1270s - 1280s 1290s 1300s 1310s 1320s
Years: 1274 1275 1276 1277 1278 - 1279 - 1280 1281 1282 1283 1284
Deaths
... for details. Derivation The quadratic formula is derived by the method of completing the square[?]. <math>ax^2+bx+c=0</math> Dividing o ...