TY - JOUR AU - L. A. Cherkas TI - Conditions for the center for certain equations of the form $yy'=P(x)+Q(x)y+R(x)y^2$ JO - Differencialʹnye uravneniâ PY - 1972 SP - 1435 EP - 1439 VL - 8 IS - 8 PB - mathdoc UR - http://geodesic.mathdoc.fr/item/DE_1972_8_8_a12/ LA - ru ID - DE_1972_8_8_a12 ER -