答： x0,f(x)=ln(b+x^2) x=0处f(x)连续,则有：f(0-) =(x→0-)lim2a(1-cosx)/x^2 =(x→0-)lim2asinx/(2x) =a=1 f(0+) =(x→0+)lim ln(b+x^2) =lnb=1 b=e 综上所述,a=1,b=e
