function f = area_multiplier_volume( q )
% –Ú“IŠÖ�”�i’¼•û‘Ì‚Ì•\–Ê�Ï + –¢’è�æ�”*“™Ž®�§–ñ�j
% q(1:4) = x, y, z, \lambda
% 2(xy+yz+zx) + \lambda (xyz-5^3)
    x = q(1); y = q(2); z = q(3); lambda = q(4);
    f = 2*(x*y+y*z+z*x) + lambda*(x*y*z-5^3);
end
