Given three strictly positive real numbers a,b,c and two strictly positive real numbers d,e such that:
a2+b2+c2=d2+e2,
a4+b4+c4=d4+e4.
We need to compare a3+b3+c3 with d3+e3.
### Step 1: Use the Known Equalities
We have been given the equalities involving squares and fourth powers:
1. a2+b2+c2=d2+e2 — This tells us that the sum of the squares of a,b,c equal those of d,e.
2. a4+b4+c4=d4+e4 — This similarly extends to the fourth powers.
### Step 2: Apply Power Mean Inequality
The Power Mean Inequality states that for any non-negative numbers x1,x2,…,xn and any real numbers p<q,
(nx1p+x2p+⋯+xnp)1/p≤(nx1q+x2q+⋯+xnq)1/q.
#### Applying the Inequality:
- Let us apply this inequality to the sequences a,b,c and d,e with p=3 and q=4.
- For a,b,c:
(3a3+b3+c3)1/3≤(3a4+b4+c4)1/4.
- For d,e:
(2d3+e3)1/3≤(2d4+e4)1/4.
### Step 3: Analyzing Our Equations
Given a4+b4+c4=d4+e4, the right sides of the inequalities are equal, which gives us:
(3a4+b4+c4)1/4=(2d4+e4)1/4.
Since 3a3+b3+c3 measure follows the cube root mean of smaller numbers due to the positive nature and similar inequality holds for such values compared to fewer larger cubes in d3+e3:
d3+e3≥a3+b3+c3.
Thus, the comparison yields:
d3+e3≥a3+b3+c3.