lim 1/sin^2(x)--cos^2(x)/x^2=lim [x^2-1/4sin^2(2x)]/[x^2 sin^2(x)] =lim [x^2-1/4sin^2(2x)]/x^4 sinx~x(等价无穷小)=lim[2x-sin2xcos2x]/(4x^3) 罗比达法则=lim[2x-1/2sin4x]/(4x^3)=lim[2-2cos4x]/(12x^2) 罗...