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In [1], the authors established the Brunn-Minkowski inequality for centroid body. In this paper, we give an isolate form and volume difference of it, respectively. Both of these results are strength versions of the original.

The setting for this paper is n-dimensional Euclidean space. Let denote the set of convex bodies (compact, convex subsets with non-empty interiors). Let and denote the unit ball and unit sphere in, respectively. If, then the support function of K, , is defined by

where denotes the standard inner product of u and x.

For each compact star-shaped about the origin, denoted by its n-dimensional volume. The centroid body of K is the origin-symmetric convex body whose support function is given by (see [

where the integration is with respect to Lebesgue measure on.

Centroid body was attributed by Blaschke and Dupin (see [3,4]), it was defined and investigated by Petty [

For star body K and L, let denote the harmonic Blaschke addition of K and L. In [

Theorem A. Let be star bodies in. Then

the equality holds if and only if and are homothetic.

In this paper, we give two strength versions of (1.3). Our main results are the following two theorems.

Theorem 1.1. Let be star bodies in and.

the equality holds if and only if and are homothetic.

Theorem 1.2. Let and be star bodies in. Ellipsoid, and is a homothetic copy of. Then

the equality holds if and only if and are homothetic and

where is a constant.

Remark. Let or in Theorem 1.1, or let in Theorem 1.2, we can both get the Theorem A.

For a compact subset of, with the origin in its interior, star-shaped with respect to the origin, the radial function, is defined by

If is continuous and positive, L will be called a star body. Let denote the set of star bodies in.

The mixed volume of the compact convex subsets of is defined by

If, , then

will be denote as

. If, then is called the quermassintegrals of; it will often be written as.

The mixed quermassintegrals

of, are defined by [

Since, it follows that

, for all i. Since the quermassintegrals is Minkowski linear, it follows that

for all K.

Aleksandrov [

for all. The measure is independent of the body and is just ordinary Lebesgue measure, S on. The surface area measure will frequently be written simply as.

Suppose, and are nonnegative real numbers and not both zero. To define the harmonic Blaschke addition, , first define by [

The body is defined as the body whose radial function is given by

In this section, we will establish the inequality more general than Theorem 1.1 as follows.

Theorem 3.1. Let, and . Then

with equality holds if and only if and are homothetic.

To prove Theorem 3.1, the following preliminary results will be needed:

Lemma 3.2. ([

with equality if and only if K and L are homothetic.

Lemma 3.3. ([

with equality if and only if K and L are homothetic.

Proof of Theorem 3.1.

By (2.4), (2.5) and the polar coordinate formula for volume, we can get Hence from (2.5), we obtain

Using polar coordinates, (1.2) can be written as an integral over

Then from (3.3) and (3.4), we have

For and. Let

By (2.3) and (3.5), we have

That is

By Lemma 3.2, we get

which implies that,

with equality holds if and only if and are homothetic.

The Brunn-Minkowski inequality (3.2) can now be used to conclude that

with equality holds if and only if F and G are homothetic.

By (3.7) and (3.8), we get the first inequality of Theorem 3.1. By the equality conditions of (3.7) and (3.8), the first equality of Theorem 3.1 holds if and only if and are homothetic.

By (3.5) and Lemma 3.3, we get

Similarly,

Hence,

with equality holds if and only if and are homothetic. This completes the proof.

Let in Theorem 3.1, we obtain an isolate form of Brunn-Minkowski inequality for centroid body.

Corollary 3.4. Let be star bodies in and.

the equality holds if and only if and are homothetic.

Now, we establish the volume difference of BrunnMinkowski inequality for centroid body.

Theorem 3.5. Let and be star bodies in. Ellipsoid, and is a homothetic copy of. Then

the equality holds if and only if and are homothetic and

where is a constant.

To prove Theorem 3.5, we need the following two lemmas:

Lemma 3.6. (Bellman’s inequality) ([

Then

with equality if and only if, where is a constant.

Lemma 3.7. (Busemann-Petty centroid inequality) ([

with equality if and only if is a centered ellipsoid.

Proof of Theorem 1.2. Applying inequality (1.3), we have

the equality holds if and only if and are homothetic.

From (3.9) and (3.10), we obtain that

Since and by Lemma 3.7, we get

and

By (3.11) and Bellman’s inequality, we get

By the equality conditions of (3.9) and the Bellman’s inequality, the equality of (3.12) holds if and only if and are homothetic and

where is a constant. This completes the proof.

The authors would like to acknowledge the support from the National Natural Science Foundation of China (11101216, 11161024), Qing Lan Project and the Nanjing Xiaozhuang University (2009XZRC05, 2010KYQN24).