reserve f,f1,f2,g for PartFunc of REAL,REAL;
reserve A for non empty closed_interval Subset of REAL;
reserve p,r,x,x0 for Real;
reserve n for Element of NAT;
reserve Z for open Subset of REAL;

theorem Th11:
  arcsin (-sqrt 2/2) = -PI/4
proof
  PI/4 < PI/2 by XREAL_1:76;
  then (PI/4)*(-1) > (PI/2)*(-1) by XREAL_1:69;
  hence thesis by Th8,SIN_COS6:69;
end;
