对x求导得到1-y' +0.5cosy *y'=0所以y'=1/(1-0.5cosy)再继续求导得到y"= -1/(1-0.5cosy)^2 *(1-0.5cosy)'= -1/(1-0.5cosy)^2 * 0.5siny *y'= -1/(1-0.5cosy)^2 * 0.5siny *1/(1-0.5cosy)= -0.5siny/(1-0.5cosy)^3...