54911312
For each integral, identify the most useful first algebraic move: polynomial long division, completing the square, or neither. Do not evaluate.
a) \(\int\frac{x^2+1}{x-1}\,\text{d}x\)
b) \(\int\frac{1}{x^2+6x+13}\,\text{d}x\)
c) \(\int\frac{2x}{x^2+1}\,\text{d}x\)
d) \(\int\frac{x+3}{x^2+6x+13}\,\text{d}x\)
Hints
- Compare numerator and denominator degrees before choosing any other method.
- For a quadratic denominator, ask whether rewriting it around its vertex reveals a standard form.
- Also check whether the numerator already relates directly to the denominator’s derivative.
Solution
1. a) The numerator's degree is at least the denominator's degree, so use polynomial long division.
2. b) The quadratic denominator is irreducible in its given form and becomes \((x+3)^2+4\), so complete the square.
3. c) The numerator is the derivative of the denominator up to a constant factor, so neither listed rearrangement is needed.
4. d) The numerator matches half the derivative of the denominator, so neither rearrangement is needed before integrating.
Answer
a) Polynomial long division
b) Completing the square
c) Neither
d) Neither
