Decades: 1230s 1240s 1250s 1260s 1270s - 1280s - 1290s 1300s 1310s 1320s 1330s
Years: 1277 1278 1279 1280 1281 - 1282 - 1283 1284 1285 1286s[?] 1287
Births
Deaths
... 4a2. We get <math>\left(x+\frac{b}{2a}\right)^2=\frac{-4ac+b^2}{4a^2}=\frac{b^2-4ac}{4a^2}.</math> Taking square roots of bo ...