Integrals Evaluation 0Cec31
1. Evaluate $$\int_0^1 x \sin(x^2) \, dx$$
- Use substitution: let $$u = x^2$$, then $$du = 2x \, dx$$ or $$x \, dx = \frac{du}{2}$$.
- Change limits: when $$x=0$$, $$u=0$$; when $$x=1$$, $$u=1$$.
- Integral becomes $$\int_0^1 \sin(u) \frac{du}{2} = \frac{1}{2} \int_0^1 \sin(u) \, du$$.
- Integrate: $$\int \sin(u) \, du = -\cos(u) + C$$.
- Evaluate definite integral: $$\frac{1}{2}[-\cos(u)]_0^1 = \frac{1}{2}[-\cos(1) + \cos(0)] = \frac{1}{2}(1 - \cos(1))$$.
2. Evaluate $$\int \frac{5}{(x+3)(x-2)} \, dx$$
- Use partial fractions: $$\frac{5}{(x+3)(x-2)} = \frac{A}{x+3} + \frac{B}{x-2}$$.
- Multiply both sides by denominator: $$5 = A(x-2) + B(x+3)$$.
- Set $$x=2$$: $$5 = A(0) + B(5) \Rightarrow B = 1$$.
- Set $$x=-3$$: $$5 = A(-5) + B(0) \Rightarrow A = -1$$.
- Integral becomes $$\int \left( \frac{-1}{x+3} + \frac{1}{x-2} \right) dx = -\ln|x+3| + \ln|x-2| + C = \ln\left| \frac{x-2}{x+3} \right| + C$$.
3. Evaluate $$\int_0^1 \int_0^z \int_0^y x \, dx \, dy \, dz$$
- Inner integral: $$\int_0^y x \, dx = \left[ \frac{x^2}{2} \right]_0^y = \frac{y^2}{2}$$.
- Middle integral: $$\int_0^z \frac{y^2}{2} \, dy = \frac{1}{2} \left[ \frac{y^3}{3} \right]_0^z = \frac{z^3}{6}$$.
- Outer integral: $$\int_0^1 \frac{z^3}{6} \, dz = \frac{1}{6} \left[ \frac{z^4}{4} \right]_0^1 = \frac{1}{24}$$.
4. Evaluate $$\int \frac{x+1}{\sqrt{x}} \, dx$$
- Rewrite integrand: $$\frac{x}{\sqrt{x}} + \frac{1}{\sqrt{x}} = x^{1/2} + x^{-1/2}$$.
- Integrate termwise: $$\int x^{1/2} \, dx = \frac{2}{3} x^{3/2} + C$$ and $$\int x^{-1/2} \, dx = 2 x^{1/2} + C$$.
- Sum: $$\frac{2}{3} x^{3/2} + 2 x^{1/2} + C$$.
5. Evaluate $$\int \frac{1}{16 + x^2} \, dx$$
- Use formula: $$\int \frac{1}{a^2 + x^2} \, dx = \frac{1}{a} \arctan\left( \frac{x}{a} \right) + C$$.
- Here, $$a=4$$.
- Result: $$\frac{1}{4} \arctan\left( \frac{x}{4} \right) + C$$.
6. Evaluate $$\int x \sin x \, dx$$
- Use integration by parts: let $$u = x$$, $$dv = \sin x \, dx$$.
- Then $$du = dx$$, $$v = -\cos x$$.
- Integral: $$uv - \int v \, du = -x \cos x + \int \cos x \, dx = -x \cos x + \sin x + C$$.
7. Find area bounded by $$x = y^2$$ and $$x = 8 - y^2$$
- Set equal: $$y^2 = 8 - y^2 \Rightarrow 2 y^2 = 8 \Rightarrow y^2 = 4 \Rightarrow y = \pm 2$$.
- Area between curves: $$\int_{-2}^2 [(8 - y^2) - y^2] \, dy = \int_{-2}^2 (8 - 2 y^2) \, dy$$.
- Integrate: $$\left[ 8y - \frac{2 y^3}{3} \right]_{-2}^2 = \left(16 - \frac{16}{3}\right) - \left(-16 + \frac{16}{3}\right) = 32 - \frac{32}{3} = \frac{64}{3}$$.
8. Find displacement from $$t=1$$ to $$t=2$$ for velocity $$v = \frac{t+1}{(t^2 + 2t)^2}$$
- Displacement: $$\int_1^2 \frac{t+1}{(t^2 + 2t)^2} \, dt$$.
- Note $$t^2 + 2t = t(t+2)$$.
- Let $$u = t^2 + 2t$$, then $$du = (2t + 2) dt = 2(t+1) dt$$.
- So $$dt = \frac{du}{2(t+1)}$$.
- Substitute: $$\int \frac{t+1}{u^2} dt = \int \frac{t+1}{u^2} \cdot \frac{du}{2(t+1)} = \frac{1}{2} \int u^{-2} du = \frac{1}{2} \left(-u^{-1}\right) + C = -\frac{1}{2u} + C$$.
- Evaluate definite integral: $$\left[-\frac{1}{2(t^2 + 2t)}\right]_1^2 = -\frac{1}{2(4 + 4)} + \frac{1}{2(1 + 2)} = -\frac{1}{16} + \frac{1}{6} = \frac{5}{48}$$.
Final answers:
1. $$\frac{1}{2}(1 - \cos(1))$$
2. $$\ln\left| \frac{x-2}{x+3} \right| + C$$
3. $$\frac{1}{24}$$
4. $$\frac{2}{3} x^{3/2} + 2 x^{1/2} + C$$
5. $$\frac{1}{4} \arctan\left( \frac{x}{4} \right) + C$$
6. $$-x \cos x + \sin x + C$$
7. $$\frac{64}{3}$$
8. $$\frac{5}{48}$$