Math Problem Statement

If w^3+x^3+y^3+z^3=10 show that w^4+x^4+ y^4+z^4>^3√2500

Solution

We are given the equation w3+x3+y3+z3=10w^3 + x^3 + y^3 + z^3 = 10, and we are asked to show that w4+x4+y4+z4>25003w^4 + x^4 + y^4 + z^4 > \sqrt[3]{2500}.

Step 1: Jensen's Inequality

We will use Jensen's Inequality for convex functions to help bound the expression w4+x4+y4+z4w^4 + x^4 + y^4 + z^4. First, observe that the function f(t)=t4f(t) = t^4 is convex because its second derivative is positive for all tt (since f(t)=12t2f''(t) = 12t^2).

Step 2: Apply Jensen’s Inequality

For convex functions, Jensen's inequality states that for non-negative numbers a,b,c,da, b, c, d, we have: f(a+b+c+d4)f(a)+f(b)+f(c)+f(d)4.f\left( \frac{a + b + c + d}{4} \right) \leq \frac{f(a) + f(b) + f(c) + f(d)}{4}. In our case, applying this to the function f(t)=t4f(t) = t^4, we get: (w3+x3+y3+z34)4w4+x4+y4+z44.\left( \frac{w^3 + x^3 + y^3 + z^3}{4} \right)^4 \leq \frac{w^4 + x^4 + y^4 + z^4}{4}. Since we are given that w3+x3+y3+z3=10w^3 + x^3 + y^3 + z^3 = 10, this becomes: (104)4w4+x4+y4+z44,\left( \frac{10}{4} \right)^4 \leq \frac{w^4 + x^4 + y^4 + z^4}{4}, which simplifies to: (2.5)4w4+x4+y4+z44.\left( 2.5 \right)^4 \leq \frac{w^4 + x^4 + y^4 + z^4}{4}.

Step 3: Simplifying

Now calculate 2.542.5^4: 2.54=(2.5×2.5)×(2.5×2.5)=6.25×6.25=39.0625.2.5^4 = (2.5 \times 2.5) \times (2.5 \times 2.5) = 6.25 \times 6.25 = 39.0625. Thus, we have: 39.0625w4+x4+y4+z44.39.0625 \leq \frac{w^4 + x^4 + y^4 + z^4}{4}. Multiplying both sides by 4, we get: 156.25w4+x4+y4+z4.156.25 \leq w^4 + x^4 + y^4 + z^4.

Step 4: Comparing with 25003\sqrt[3]{2500}

Now we compute 25003\sqrt[3]{2500}. We know that 25001/32500^{1/3} is approximately: 2500313.58.\sqrt[3]{2500} \approx 13.58.

Finally, observe that: w4+x4+y4+z4156.25>13.58,w^4 + x^4 + y^4 + z^4 \geq 156.25 > 13.58, which shows that: w4+x4+y4+z4>25003.w^4 + x^4 + y^4 + z^4 > \sqrt[3]{2500}.

Thus, we have shown that w4+x4+y4+z4>25003w^4 + x^4 + y^4 + z^4 > \sqrt[3]{2500}.


Would you like a more detailed explanation of any step or have any specific questions?

Here are 5 related questions to deepen your understanding:

  1. What are the conditions under which Jensen’s inequality can be applied?
  2. How do we calculate the cube root of a number like 2500 more accurately?
  3. What makes a function convex, and why is this important for inequalities?
  4. Can this method be applied to other powers, such as w5+x5+y5+z5w^5 + x^5 + y^5 + z^5?
  5. How does the choice of w3+x3+y3+z3=10w^3 + x^3 + y^3 + z^3 = 10 affect the final inequality?

Tip: Convex functions grow faster than linear ones, which is why Jensen’s inequality helps to bound sums of powers effectively.

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Math Problem Analysis

Mathematical Concepts

Algebra
Inequalities
Convex Functions

Formulas

Jensen's inequality: f((a+b+c+d)/4) ≤ (f(a) + f(b) + f(c) + f(d))/4
w^3 + x^3 + y^3 + z^3 = 10

Theorems

Jensen's Inequality

Suitable Grade Level

Grades 11-12