⒈ln(x²+y²)=2arc tan(y/x),
(2xdx+2ydy)/(x²+y²)=2[1/(1+y²/x²)](xdy-ydx)/x²=2(xdy-ydx)/(x²+y²)
xdx+ydy=xdy-ydx,(x-y)dy=(x+y)dx,dy/dx=(x+y)/(x-y)选择(C)
⒉y=x^sinx,lny=(sinx)lnx,y'/y=(cosx)lnx+(sinx)/x选择(D)
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