Prove that f(x) = 5x? + 3x – 26 is 0(x²). %3D

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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**Problem Statement:**

Prove that \( f(x) = 5x^2 + 3x - 26 \) is \( \theta(x^2) \).

---

Follow the steps below to prove that the given function \( f(x) \) belongs to the asymptotic notation \( \theta(x^2) \).

1. **Definition of \( \theta \)-notation:**

   A function \( f(x) \) is said to be \( \theta(g(x)) \) if there are positive constants \( c_1 \), \( c_2 \), and \( n_0 \) such that for all \( x \geq n_0 \),
   \[
   c_1 g(x) \leq f(x) \leq c_2 g(x)
   \]

2. **Apply the definition to \( f(x) \):**

   We need to show that there exist constants \( c_1 \), \( c_2 \), and \( n_0 \) such that
   \[
   c_1 x^2 \leq 5x^2 + 3x - 26 \leq c_2 x^2
   \]
   for all \( x \geq n_0 \).

3. **Find the upper bound:**
   
   To find an upper bound, observe that the term \( 5x^2 \) will dominate for larger values of \( x \). Therefore,
   \[
   5x^2 + 3x - 26 \leq 5x^2 + 3x
   \]
   \[
   5x^2 + 3x \leq 5x^2 + 3x \leq 6x^2 \quad \text{(for sufficiently large x)}
   \]
   For \( c_2 = 6 \), let's find \( n_0 \) where this is valid. For large \( x \), \( 3x \) becomes negligible compared to \( 5x^2 \).

4. **Find the lower bound:**

   Similarly, for the lower bound:
   \[
   5x^2 + 3x - 26 \geq 5x^2 - 26
   \]
   \[
   5x^2 - 26 \geq 4x
Transcribed Image Text:**Problem Statement:** Prove that \( f(x) = 5x^2 + 3x - 26 \) is \( \theta(x^2) \). --- Follow the steps below to prove that the given function \( f(x) \) belongs to the asymptotic notation \( \theta(x^2) \). 1. **Definition of \( \theta \)-notation:** A function \( f(x) \) is said to be \( \theta(g(x)) \) if there are positive constants \( c_1 \), \( c_2 \), and \( n_0 \) such that for all \( x \geq n_0 \), \[ c_1 g(x) \leq f(x) \leq c_2 g(x) \] 2. **Apply the definition to \( f(x) \):** We need to show that there exist constants \( c_1 \), \( c_2 \), and \( n_0 \) such that \[ c_1 x^2 \leq 5x^2 + 3x - 26 \leq c_2 x^2 \] for all \( x \geq n_0 \). 3. **Find the upper bound:** To find an upper bound, observe that the term \( 5x^2 \) will dominate for larger values of \( x \). Therefore, \[ 5x^2 + 3x - 26 \leq 5x^2 + 3x \] \[ 5x^2 + 3x \leq 5x^2 + 3x \leq 6x^2 \quad \text{(for sufficiently large x)} \] For \( c_2 = 6 \), let's find \( n_0 \) where this is valid. For large \( x \), \( 3x \) becomes negligible compared to \( 5x^2 \). 4. **Find the lower bound:** Similarly, for the lower bound: \[ 5x^2 + 3x - 26 \geq 5x^2 - 26 \] \[ 5x^2 - 26 \geq 4x
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