Plz explain this encircled expression

Expression for AH. We have AH = A (U + PV) = AU+ A (PV stituting the value of AU and P from eqns. (9) and (2), we get nRT an2 AH =-an| +A V-nb y2 V2 V-nb V V-nb = -an2 + nRT -an V, -nb +nb V -nb + nb +nRT V. V V, -nb = -2an V-nb nb nb =-2an +nRT 1+ 1+ V -nb V-nb 1 1 AH =-2an v, +n2 bRTI ..(11) V,-nb V-nb