Question

Difficulty: MediumIndefinite Integration of Polynomial and Trigonometric Functions

What is the result of evaluating the indefinite integral ((2x1)26cos(2x))dx\int \left( (2x - 1)^2 - 6\cos(2x) \right) \, dx?

  1. 43x32x2+x3sin(2x)+C\frac{4}{3}x^3 - 2x^2 + x - 3\sin(2x) + CAnswer
  2. B
    43x32x2+x3sin(2x)\frac{4}{3}x^3 - 2x^2 + x - 3\sin(2x)
  3. C
    43x32x2+x+3sin(2x)+C\frac{4}{3}x^3 - 2x^2 + x + 3\sin(2x) + C
  4. D
    43x32x2+x12sin(2x)+C\frac{4}{3}x^3 - 2x^2 + x - 12\sin(2x) + C

Answer

43x32x2+x3sin(2x)+C\frac{4}{3}x^3 - 2x^2 + x - 3\sin(2x) + C
Expanding the squared term (2x1)2(2x - 1)^2 yields 4x24x+14x^2 - 4x + 1. Integrating term by term using the power rule gives 43x32x2+x\frac{4}{3}x^3 - 2x^2 + x. The integral of 6cos(2x)-6\cos(2x) is 62sin(2x)=3sin(2x)-\frac{6}{2}\sin(2x) = -3\sin(2x). Adding the arbitrary constant CC results in 43x32x2+x3sin(2x)+C\frac{4}{3}x^3 - 2x^2 + x - 3\sin(2x) + C.

Step-by-Step Solution

1
Expand the squared binomial term inside the integral
(2x1)2=4x24x+1(2x - 1)^2 = 4x^2 - 4x + 1
Expanding the expression allows for term-by-term integration using standard integration rules.
2
Integrate each term of the expanded polynomial
\int (4x^2 - 4x + 1) \, dx = \frac{4}{3}x^3 - 2x^2 + x
Apply the power rule for integration: \int x^n \, dx = \frac{x^{n+1}}{n+1}.
3
Integrate the trigonometric term
\int -6\cos(2x) \, dx = -6 \cdot \frac{1}{2}\sin(2x) = -3\sin(2x)
The standard integral of \cos(kx) is \frac{1}{k}\sin(kx).
4
Combine all integrated terms and append the constant of integration
\frac{4}{3}x^3 - 2x^2 + x - 3\sin(2x) + C
Indefinite integration requires an arbitrary constant of integration C.

Key Concept

Indefinite Integration of Polynomial and Trigonometric Functions
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