用洛必达法则计算极限：limx→0 (e^x-cosx)/(sinx)
lim x→π (sin3x)/(tan5x);lim x→0 (e^x+e^[-x]-2)/(1-cosx) ;lim x→0 [x(e^x+1)-2(e^x-1)]/x^3 ;lim x→π/2 (Insinx)/(π-2x)^2