y"'²-y"y""=0化为:(y"'²-y"y"")/y"'²=0即:(y"/y"')'=0积分:y"/y"'=C1C1y"'-y"=0特征方程为C1r³-r²=0得r=0(为二重根), 1/C1故通解y=C2x+C3+C4e^(x/C1)