简单计算一下即可，答案如图所示
x-y+1/2siny=0 两边对x求导得 1-y'+1/2cosy*y'=0 y'=2/(2-cosy) y''=dy'/dx =(dy'/dy)*(dy/dx) =[-2/(2-cosy)²]*siny*2/(2-cosy) =-4siny/(2-cosy)³
