#\ \ \ \ \ \ lim_(x->0)x/sqrt(1-cos(x))#
#=lim_(x->0)x/sqrt(1-cos(x))*sqrt(1+cos(x))/sqrt(1+cos(x))#
#=lim_(x->0)(xsqrt(1+cos(x)))/sqrt(1-cos^2(x))#
#=lim_(x->0)(xsqrt(1+cos(x)))/sin(x)#
#=lim_(x->0)x/sin(x)sqrt(1+cos(x))#
#=lim_(x->0)x/sin(x)*lim_(x->0)sqrt(1+cos(x))#
#=1*sqrt(2)#
#=sqrt(2)#