Decades: 1220s 1230s 1240s 1250s 1260s - 1270s - 1280s 1290s 1300s 1310s 1320s
Years: 1270 1271 1272 1273 1274 - 1275 - 1276 1277 1278 1279 1280
Births
Deaths
... by a, we have <math> x^2 + \left( \frac{b}{a} \right) x + \frac{c}{a}=0 </math> which is equivalen ...