One method is to directly use Robida's law for deformation. According to your formula, the limit is 0/0. After deduction, the original limit = lim (-2x)/[-(CSC (π x/2) 2× π/2) = 4/π× lim x * (sin (π x/2) 2.

Another way is to simplify writing, and then consider using Robida's law or equivalent infinitesimal. The purpose of simplification is to find out the product factors with non-zero limits and calculate these limits first. Original limit = lim (1+x) (1-x) * sin (π x/2)/cos (π x/2) = lim (1+x) * sin (π x/2) × lim (/kloc-)