例1P164972 af可fax, of ay af of cos+sin e ar Ox ar ay ar 0. 今”r ax a 2 af ∴左式 2兀 2兀 limdel-o 2兀g-00 2086→0JodB/g In e dr A im[2m lf(cose, sinO)-f(ecos, e sin 0)de E→>0 2丌 2r 6-0 Jo -f(ecos,Esin 0)de =lim f(acos,, esin 6)=f(0, 0) →0例1 P164 9.72r y y f r x x f r f     +     =   cos sin y f x f   +   = r r f    y y f x x f   +   = dr r r f r d    →       −  = 2 0 1 2 2 0 lim 2 1 左式           lim [ f (cos ,sin ) f ( cos , sin )]d 2 1 2 0 0 − − =  →         lim f ( cos , sin )d 2 1 2 0 0 − − =  → lim ( cos , sin ) (0,0) 0 0 0 = f = f →      dr r f d    →     − = 2 1 0 0 lim 2 1