Decades: 1220s 1230s 1240s 1250s 1260s - 1270s - 1280s 1290s 1300s 1310s 1320s
Years: 1271 1272 1273 1274 1275 - 1276 - 1277 1278 1279 1280 1281
Births
Deaths
... use a polar coordinate system, assume a constant radius, and take two derivatives. Let r(t) be a vector that describes the position of a point mass as a function of ...