Decades: 1130s 1140s 1150s 1160s 1170s - 1180s - 1190s 1200s 1210s 1220s 1230s
Years: 1177 1178 1179 1180 1181 - 1182 - 1183 1184 1185 1186 1187
Births
Deaths
... is zero, then there is a repeated solution x, and this solution is real. (Geometrically, this means that the parabola described by the quadratic equation touches the ...