Expression 4: "b" equals secant squared left parenthesis, mod left parenthesis, arctan left parenthesis, "P" . "y" , "P" . "x" , right parenthesis , StartFraction, 2 pi Over "n" , EndFraction , right parenthesis minus StartFraction, pi Over "n" , EndFraction , right parenthesis minus "P" . "x" squared minus "P" . "y" squaredb=sec2modarctanP.y,P.x,2πn−πn−P.x2−P.y2