x趋于零时,limf(x)=(1-cos2x)/x=2*(sinx)^2/x=0.x=0时,f(x)=0.limf(x)=f(0)=0,故函数在x=0处连续.f'(0)=limf(x)/x=(1-cos2x)/x^2=2*(sinx)^2/x^2=2.当x不等于零时,f'(x)=(2x*sin2x-1+cos2x)/x^2当x趋于零时（左趋还...