∵cosxsinydy=cosysinxdx
==>sinydy/cosy=sinxdx/cosx
==>d(cosy)/cosy=d(cosx)/cosx
==>ln│cosy│=ln│cosx│+ln│C│ (C是积分常数)
==>cosy=C*cosx
∴原方程的通解是cosy=C*cosx (C是积分常数)
∵当x=0时,y=π/4
∴cos(π/4)=C*cos(0)
==>C=1/√2
故原方程满足初始条件的特解是cosy=cosx/√2.