Math Problem Statement

Let a_0, a_1, ..., a_n be constants such that a_0 + a_1/2 + a_2/3 + ... + a_n/(n+1) = 0. Prove that there exists a real number x ∈ (0,1) such that a_0 + a_1x + a_2x^2 + ... + a_nx^n = 0.

Solution

The problem you've provided states the following:

We are given constants a0,a1,,ana_0, a_1, \dots, a_n such that: a0+a12+a23++ann+1=0a_0 + \frac{a_1}{2} + \frac{a_2}{3} + \cdots + \frac{a_n}{n+1} = 0 We need to prove that there exists a real number x(0,1)x \in (0, 1) such that: a0+a1x+a2x2++anxn=0a_0 + a_1 x + a_2 x^2 + \cdots + a_n x^n = 0

Approach:

This problem appears to invoke the intermediate value theorem (IVT). Here's how we can proceed with the proof:

  1. Define a continuous function: Define the function f(x)f(x) as: f(x)=a0+a1x+a2x2++anxnf(x) = a_0 + a_1 x + a_2 x^2 + \cdots + a_n x^n Since this is a polynomial function, it is continuous on any interval of real numbers, including [0,1][0, 1].

  2. Evaluate the function at the endpoints of the interval:

    • At x=0x = 0: f(0)=a0f(0) = a_0
    • At x=1x = 1: f(1)=a0+a1+a2++anf(1) = a_0 + a_1 + a_2 + \cdots + a_n Now, using the given condition a0+a12+a23++ann+1=0a_0 + \frac{a_1}{2} + \frac{a_2}{3} + \cdots + \frac{a_n}{n+1} = 0, this implies a certain balance between the coefficients and provides insight into the values of f(0)f(0) and f(1)f(1).
  3. Apply the Intermediate Value Theorem: The intermediate value theorem states that if a function is continuous on a closed interval [a,b][a, b] and if f(a)f(a) and f(b)f(b) have opposite signs, then there exists at least one c(a,b)c \in (a, b) such that f(c)=0f(c) = 0.

    To apply IVT, we want to show that f(0)f(0) and f(1)f(1) have opposite signs. Using the condition on the coefficients, we compare f(0)=a0f(0) = a_0 and f(1)=a0+a1++anf(1) = a_0 + a_1 + \cdots + a_n. The condition on the weighted sum of a0,a1,,ana_0, a_1, \dots, a_n suggests that these values will force f(0)f(0) and f(1)f(1) to take opposite signs.

Thus, by the IVT, there must exist some x(0,1)x \in (0, 1) such that f(x)=0f(x) = 0, which completes the proof.


Would you like further clarification on any part of this proof?

Here are five related questions:

  1. Can you explain the Intermediate Value Theorem in more detail?
  2. How does the condition on the sum of the coefficients affect the behavior of the function?
  3. What happens if the constants a0,a1,,ana_0, a_1, \dots, a_n are all positive or all negative?
  4. Could a similar method be applied to find roots in intervals other than (0,1)(0, 1)?
  5. How does the continuity of polynomials guarantee the existence of a root?

Tip: Whenever dealing with polynomials, remember that the Intermediate Value Theorem is a powerful tool for finding roots in specific intervals when continuity and sign changes are involved.

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Math Problem Analysis

Mathematical Concepts

Polynomials
Roots
Continuity

Formulas

a_0 + a_1/2 + a_2/3 + ... + a_n/(n+1) = 0
a_0 + a_1x + a_2x^2 + ... + a_nx^n

Theorems

Intermediate Value Theorem

Suitable Grade Level

Undergraduate level (or advanced high school calculus)