Math Problem Statement

Bestimmen Sie folgendes Integral: I = ∫(x³ + 4x²) * sin(2x) dx

Solution

The task is to solve the given integral step by step using partial integration (integration by parts). Here's the process:

Integral

The integral is: I=(x3+4x2)sin(2x)dxI = \int (x^3 + 4x^2) \cdot \sin(2x) \, dx

Using Integration by Parts

Integration by parts formula: udv=uvvdu\int u \, dv = u \cdot v - \int v \, du

We split the integrand into two factors:

  • Choose u=x3+4x2u = x^3 + 4x^2, which will be differentiated (uu').
  • Choose dv=sin(2x)dxdv = \sin(2x) \, dx, which will be integrated (vv).

Steps:

  1. Differentiation of uu: u=x3+4x2,dudx=3x2+8xu = x^3 + 4x^2, \quad \frac{du}{dx} = 3x^2 + 8x

  2. Integration of dvdv: dv=sin(2x)dx,v=12cos(2x)dv = \sin(2x) \, dx, \quad v = -\frac{1}{2} \cos(2x)

Substitute into the integration by parts formula: I=uvvduI = u \cdot v - \int v \, du

  1. Substitute values: I=(12(x3+4x2)cos(2x))(12cos(2x)(3x2+8x))dxI = \left(-\frac{1}{2} (x^3 + 4x^2) \cos(2x)\right) - \int \left(-\frac{1}{2} \cos(2x) (3x^2 + 8x) \right) dx

  2. Simplify: I=12(x3+4x2)cos(2x)+12cos(2x)(3x2+8x)dxI = -\frac{1}{2} (x^3 + 4x^2) \cos(2x) + \frac{1}{2} \int \cos(2x) (3x^2 + 8x) dx

The new integral, cos(2x)(3x2+8x)dx\int \cos(2x) (3x^2 + 8x) dx, requires further application of integration by parts. Repeat the process by splitting 3x2+8x3x^2 + 8x into parts.


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Math Problem Analysis

Mathematical Concepts

Integration
Partial Integration
Trigonometric Functions

Formulas

Integration by parts: ∫u dv = u v - ∫v du

Theorems

Integration by parts theorem

Suitable Grade Level

Undergraduate Level