dy/dx+y/x=sinx/x ==> xdy + ydx = sinx dx==>咐晌前缓 xdy + ydx - sin x dx = 0==>衡悔锋 d(xy - cos x) = 0==> xy - cosx = Cy = (cosx + C)/x
xdy+ydx=sinxxy= -cosx+Cxy+cosx=C
