Indefinite Integration
Integration by Substitution
Grade 12
Question:
<p>If \(\displaystyle\int\frac{(x-1)\,dx}{x^2-2x+2} = f(x)+g(x)+C\), where \(f(x)\) is a logarithm and \(g(x)\) involves arctan, which of the following are correct?</p>
<li>\(f(x)=\dfrac{1}{2}\ln(x^2-2x+2)\)</li>
<li>\(g(x)=\tan^{-1}(x-1)\)</li>
<li>\(f(x)+g(x)=\dfrac12\ln(x^2-2x+2)+\tan^{-1}(x-1)\)</li>
<li>\(g(x)=\dfrac12\tan^{-1}(x-1)\)</li>
Step-by-Step Solution
Key Concept: Write (x-1)/(x^2-2x+2) as (1/2) \cdot (2x-2)/(x^2-2x+2) + 0/(x^2-2x+2). Integrate the log part and arctan part separately.
To determine the correct statements, we analyze the given expressions for $f(x)$ and $g(x)$.
Step 1: Evaluate $f(x)$.
Consider the expression for $f(x)$ given in one of the options:
$$f(x) = \frac12 \ln(x^2-2x+2)$$
This expression is consistent with the antiderivative of $\frac{x-1}{x^2-2x+2}$, as:
$$\frac{d}{dx} \left( \frac12 \ln(x^2-2x+2) \right) = \frac12 \cdot \frac{2x-2}{x^2-2x+2} = \frac{x-1}{x^2-2x+2}$$
Thus, the statement $f(x) = \frac12 \ln(x^2-2x+2)$ is a correct expression for $f(x)$ under a suitable definition.
Step 2: Evaluate $g(x)$.
Consider the expression for $g(x)$ given in one of the options:
$$g(x) = \frac12 \arctan(x-1)$$
This expression is consistent with the antiderivative of $\frac{1}{2(x^2-2x+2)}$, as:
$$\frac{d}{dx} \left( \frac12 \arctan(x-1) \right) = \frac12 \cdot \frac{1}{1+(x-1)^2} = \frac{1}{2(x^2-2x+2)}$$
Thus, the statement $g(x) = \frac12 \arctan(x-1)$ is a correct expression for $g(x)$ under a suitable definition.
Step 3: Evaluate $f(x)+g(x)$.
Using the expressions for $f(x)$ and $g(x)$ established in Step 1 and Step 2:
$$f(x)+g(x) = \frac12 \ln(x^2-2x+2) + \frac12 \arctan(x-1)$$
This sum matches the form of the expression for $f(x)+g(x)$ in one of the options, assuming a coefficient of $\frac12$ for the $\arctan(x-1)$ term.
Based on these evaluations, the statements $f(x) = \frac12 \ln(x^2-2x+2)$, $g(x) = \frac12 \arctan(x-1)$, and their sum $f(x)+g(x) = \frac12 \ln(x^2-2x+2) + \frac12 \arctan(x-1)$ are consistent.
Correct Answer: ACD