dB= 10 Gex sing +e, cos 0) x'=x-yctge dx'=y cse de 2Tr =y·cSe B SIn X y·Cseb.d0 2丌 vcsel 2a (x,y) (2-2) 4Ta 4a B=do a cos e y2丌-a2a.r 92 d·sinO=hLn 474g Sina 4Ta Ln-2 4a fir y cse =   2 1 2 2 1 1 0 sin 2 0 0 2 1 , 0 0 0 sin sin 0 2 1 2 2 ( ) 4 4 cos 2 2 sin 4 sin 4 4 X ycse a y a I B y cse d a I I a a I dx B a r I I d Ln a a I r Ln a r                               − = −    = − − = −  =    = = =    0 2 ( sin cos ) x dx 2 x y dI d B e e x y ctg y cse d r        = − + = −  =    