Integral Calculations
1. Problem: Calculate the integrals given in parts a, b, c, and d.
2. Part a: \(\int \sqrt{16x} \sin(1 + x^{3/2}) \, dx\)
- Rewrite \(\sqrt{16x} = 4\sqrt{x} = 4x^{1/2}\).
- Let \(u = 1 + x^{3/2}\), then \(du = \frac{3}{2} x^{1/2} dx\).
- Solve for \(x^{1/2} dx = \frac{2}{3} du\).
- Substitute: \(4x^{1/2} \sin(u) dx = 4 \sin(u) \cdot x^{1/2} dx = 4 \sin(u) \cdot \frac{2}{3} du = \frac{8}{3} \sin(u) du\).
- Integral becomes \(\int \frac{8}{3} \sin(u) du = \frac{8}{3} \int \sin(u) du = -\frac{8}{3} \cos(u) + C\).
- Substitute back \(u = 1 + x^{3/2}\).
- Final answer: \(-\frac{8}{3} \cos(1 + x^{3/2}) + C\).
3. Part b: \(\int_5^{12} x^3 \ln(6x) \, dx\)
- Use integration by parts: let \(u = \ln(6x)\), \(dv = x^3 dx\).
- Then \(du = \frac{1}{x} dx\), \(v = \frac{x^4}{4}\).
- Integration by parts formula: \(\int u dv = uv - \int v du\).
- Compute: \(= \left. \frac{x^4}{4} \ln(6x) \right|_5^{12} - \int_5^{12} \frac{x^4}{4} \cdot \frac{1}{x} dx = \left. \frac{x^4}{4} \ln(6x) \right|_5^{12} - \frac{1}{4} \int_5^{12} x^3 dx\).
- Evaluate \(\int_5^{12} x^3 dx = \left. \frac{x^4}{4} \right|_5^{12} = \frac{12^4 - 5^4}{4} = \frac{20736 - 625}{4} = \frac{20111}{4}\).
- Substitute back: \(= \frac{12^4}{4} \ln(72) - \frac{5^4}{4} \ln(30) - \frac{1}{4} \cdot \frac{20111}{4} = 10368 \ln(72) - 156.25 \ln(30) - \frac{20111}{16}\).
4. Part c: \(\int \left( \frac{1 - x^{-2}}{x^{1/2} - x^{-1/2}} - \frac{2}{x^{3/2}} + \frac{x^{-2} - x}{x^{1/2} - x^{-1/2}} \right) dx\)
- Combine fractions over common denominator \(x^{1/2} - x^{-1/2}\).
- Simplify numerator:
\(\frac{1 - x^{-2} + x^{-2} - x}{x^{1/2} - x^{-1/2}} - \frac{2}{x^{3/2}} = \frac{1 - x}{x^{1/2} - x^{-1/2}} - \frac{2}{x^{3/2}}\).
- Note \(x^{1/2} - x^{-1/2} = \frac{x - 1}{x^{1/2}}\).
- So \(\frac{1 - x}{x^{1/2} - x^{-1/2}} = \frac{1 - x}{\frac{x - 1}{x^{1/2}}} = (1 - x) \cdot \frac{x^{1/2}}{x - 1} = -x^{1/2}\).
- The integral becomes \(\int (-x^{1/2} - 2x^{-3/2}) dx = \int (-x^{1/2}) dx - 2 \int x^{-3/2} dx\).
- Integrate:
\(\int x^{1/2} dx = \frac{2}{3} x^{3/2}\),
\(\int x^{-3/2} dx = -2 x^{-1/2}\).
- So integral is \(- \frac{2}{3} x^{3/2} - 2 (-2 x^{-1/2}) + C = - \frac{2}{3} x^{3/2} + 4 x^{-1/2} + C\).
5. Part d: \(\int \frac{x + 7}{2x^2 + 9x - 18} dx\)
- Factor denominator: \(2x^2 + 9x - 18 = (2x - 3)(x + 6)\).
- Use partial fractions: \(\frac{x + 7}{(2x - 3)(x + 6)} = \frac{A}{2x - 3} + \frac{B}{x + 6}\).
- Multiply both sides by denominator:
\(x + 7 = A(x + 6) + B(2x - 3)\).
- Expand: \(x + 7 = A x + 6A + 2 B x - 3 B = (A + 2B) x + (6A - 3B)\).
- Equate coefficients:
\(A + 2B = 1\),
\(6A - 3B = 7\).
- Solve system:
From first: \(A = 1 - 2B\).
Substitute into second: \(6(1 - 2B) - 3B = 7 \Rightarrow 6 - 12B - 3B = 7 \Rightarrow -15B = 1 \Rightarrow B = -\frac{1}{15}\).
Then \(A = 1 - 2(-\frac{1}{15}) = 1 + \frac{2}{15} = \frac{17}{15}\).
- Integral becomes:
\(\int \frac{17/15}{2x - 3} dx + \int \frac{-1/15}{x + 6} dx = \frac{17}{15} \int \frac{1}{2x - 3} dx - \frac{1}{15} \int \frac{1}{x + 6} dx\).
- Integrate:
\(\int \frac{1}{2x - 3} dx = \frac{1}{2} \ln|2x - 3| + C\),
\(\int \frac{1}{x + 6} dx = \ln|x + 6| + C\).
- Final answer:
\(\frac{17}{15} \cdot \frac{1}{2} \ln|2x - 3| - \frac{1}{15} \ln|x + 6| + C = \frac{17}{30} \ln|2x - 3| - \frac{1}{15} \ln|x + 6| + C\).
Final answers:
- a) \(-\frac{8}{3} \cos(1 + x^{3/2}) + C\)
- b) \(10368 \ln(72) - 156.25 \ln(30) - \frac{20111}{16}\)
- c) \(- \frac{2}{3} x^{3/2} + 4 x^{-1/2} + C\)
- d) \(\frac{17}{30} \ln|2x - 3| - \frac{1}{15} \ln|x + 6| + C\)