lim(x->1) lncos(x-1)/[ 1- sin((π/2)x) ] (0/0)=lim(x->1) -tan(x-1)/[ -(π/2).cos((π/2)x) ] (0/0)=lim(x->1) -[sec(x-1)]^2/[ (π/2)^2.sin((π/2)x) ] =-4/π^2
