148. (2 x y cos( xy ))dx x cos( xy ) dy 0 dm ydx x m cos m dm ydx (2 x ) dx x cos( m)( )0 x x m cos m m (2 x ) dx cos m( dm dx) 0 x x m cos m m (2 x ) dx cos mdm cos mdx 0 x x 2 xdx cos mdm 0 m xy......dm xdy ydx.....dy 2 xdx cos mdm 0 x 2 sen( xy ) c