The asymptotic behavior at infinity and an estimate of positive radial solutions of the equation △u ＋ sum from i=1 to k cirli upi = 0, x ∈ Rn,（0.1）are obtained and the structure of separation property of positive radial solutions of Eq. （0.1） with different initial data α is discussed.
In this paper,we consider the inequality estimates of the positive solutions for the inhomogeneous biharmonic equation■-△^2u+u^p+f(x)=0 in R^n where △^2 is the biharmonic operator,p>1,n≥5 and 0≡f∈C(R^n)is a given nonnegative function.We obtain different inequality estimates of Eq.(*),with which the necessary conditions of existence on f and p are also established.
The existence and uniqueness of singular solutions decaying like r^-m（see （1.4）） of the equation △u＋k∑i=1ci｜x｜liupi=0,x∈R^N are obtained, wheren≥3, ci 〉0, li〉-2, i=1,2,..,k, pi〉 1, i=l,2,-..,kandthe separation structure of singular solutions decaying like r^-（n-2） of eq. （0.1） are discussed. moreover, we obtain the explicit critical exponent ps （l） （see （1.9））.
