Varied Math
1. **Problem:** Apply Simpson's rule to approximate the distance traveled for velocity data over 8 intervals between $t=0$ and $t=4$.
Simpson's rule formula with $n=8$ intervals, $h=\frac{4-0}{8}=0.5$:
$$\text{Distance} = \frac{h}{3}[v_0 + 4(v_1+v_3+v_5+v_7) + 2(v_2+v_4+v_6) + v_8]$$
Values from table:
$v_0=0, v_1=4.00, v_2=7.94, v_3=11.68, v_4=14.97, v_5=17.39, v_6=18.25, v_7=16.08, v_8=0$
Calculate:
$$4(v_1+v_3+v_5+v_7) = 4(4 + 11.68 + 17.39 + 16.08) = 4(49.15) = 196.6$$
$$2(v_2+v_4+v_6) = 2(7.94 + 14.97 + 18.25) = 2(41.16) = 82.32$$
Sum inside brackets:
$$0 + 196.6 + 82.32 + 0 = 278.92$$
Distance:
$$\frac{0.5}{3} \times 278.92 = \frac{0.5}{3} \times 278.92 = 46.49$$
2. **Problem:** Find area under $y = x^2 + 2x + 1$ from $x=1$ to $x=2$.
Integrate:
$$\int_1^2 (x^2 + 2x + 1) dx = \left[\frac{x^3}{3} + x^2 + x \right]_1^2$$
Evaluate:
$$\left(\frac{8}{3} + 4 + 2\right) - \left(\frac{1}{3} + 1 + 1\right) = \left(\frac{8}{3} + 6\right) - \left(\frac{1}{3} + 2\right) = \frac{8}{3} - \frac{1}{3} + 6 - 2 = \frac{7}{3} + 4 = \frac{19}{3} \approx 6.33$$
3. **Problem:** Show that $\frac{1}{1-\cos \theta} + \frac{1}{1+\cos \theta} = \frac{2}{\sin^2 \theta}$.
Start with left side:
$$\frac{1}{1-\cos \theta} + \frac{1}{1+\cos \theta} = \frac{(1+\cos \theta) + (1-\cos \theta)}{(1-\cos \theta)(1+\cos \theta)} = \frac{2}{1 - \cos^2 \theta}$$
Use identity $\sin^2 \theta = 1 - \cos^2 \theta$, so
$$\frac{2}{\sin^2 \theta}$$
Hence proven.
4. **Problem:** Solve for $x$ and $y$ given $(x + y) + j(x - y) = 7 + j2$.
Equate real and imaginary parts:
$$x + y = 7$$
$$x - y = 2$$
Add equations:
$$2x = 9 \Rightarrow x = 4.5$$
Substitute back:
$$4.5 + y = 7 \Rightarrow y = 2.5$$
5. **Problem:** Find $x$ in $\log_3 6 + \log_3 (x^2 - \frac{x}{2}) = 1$.
Use log sum:
$$\log_3 \biggl(6 (x^2 - \frac{x}{2}) \biggr) = 1$$
Convert:
$$6 \left(x^2 - \frac{x}{2}\right) = 3^1 = 3$$
Simplify:
$$6 \left(x^2 - \frac{x}{2} \right) = 6x^2 - 3x = 3$$
Rearrange:
$$6x^2 - 3x - 3 = 0 \Rightarrow 2x^2 - x - 1 =0$$
Solve quadratic:
$$x = \frac{1 \pm \sqrt{1 + 8}}{4} = \frac{1 \pm 3}{4}$$
Solutions:
$$x = 1, \quad x = -\frac{1}{2}$$
6. **Problem:** Solve $2x - 6x^2 + 8 = 0$.
Rearrange:
$$-6x^2 + 2x + 8 = 0 \Rightarrow 6x^2 - 2x - 8 = 0$$
Divide by 2:
$$3x^2 - x - 4 = 0$$
Use quadratic formula:
$$x = \frac{1 \pm \sqrt{1 + 48}}{6} = \frac{1 \pm 7}{6}$$
Solutions:
$$x = \frac{8}{6} = \frac{4}{3}, \quad x = -1$$
7. **Problem:** (a) Express $(4, -3)$ in polar coordinates.
Calculate:
$$r = \sqrt{4^2 + (-3)^2} = 5$$
$$\theta = \arctan\left(\frac{-3}{4}\right) \approx -0.6435 \text{ radians}$$
Polar coordinates:
$$(5, -0.6435)$$
(b) Convert $(5, 124^\circ)$ to Cartesian:
$$x = 5 \cos 124^\circ \approx 5 \times (-0.5592) = -2.796$$
$$y = 5 \sin 124^\circ \approx 5 \times 0.8290 = 4.145$$
Cartesian coordinates:
$$(-2.796, 4.145)$$
8. **Problem:** Compute integral $\int \frac{\ln x}{x} dx$.
Use substitution:
$$u = \ln x \Rightarrow du = \frac{1}{x} dx$$
So:
$$\int u \, du = \frac{u^2}{2} + C = \frac{(\ln x)^2}{2} + C$$
9. **Problem:** Find angle between vectors $\vec{A} = 2\vec{i} + 3\vec{j} + \vec{k}$ and $\vec{B} = -\vec{i} + 4\vec{j} + 2\vec{k}$.
Dot product:
$$\vec{A} \cdot \vec{B} = 2(-1) + 3(4) + 1(2) = -2 + 12 + 2 = 12$$
Magnitudes:
$$|\vec{A}| = \sqrt{2^2 + 3^2 + 1^2} = \sqrt{14}$$
$$|\vec{B}| = \sqrt{(-1)^2 + 4^2 + 2^2} = \sqrt{21}$$
Angle $\theta$:
$$\cos \theta = \frac{\vec{A} \cdot \vec{B}}{|\vec{A}| |\vec{B}|} = \frac{12}{\sqrt{14} \sqrt{21}} = \frac{12}{\sqrt{294}} = \frac{12}{17.1756} = 0.699$$
$$\theta = \arccos(0.699) \approx 45.57^\circ$$
10. **Problem:** Prove the hyperbolic identity $\cosh^2 x - \sinh^2 x = 1$.
Recall:
$$\cosh x = \frac{e^x + e^{-x}}{2}, \quad \sinh x = \frac{e^x - e^{-x}}{2}$$
Compute:
$$\cosh^2 x - \sinh^2 x = \left(\frac{e^x + e^{-x}}{2}\right)^2 - \left(\frac{e^x - e^{-x}}{2}\right)^2$$
$$= \frac{(e^{2x} + 2 + e^{-2x}) - (e^{2x} - 2 + e^{-2x})}{4} = \frac{4}{4} = 1$$
**Final answers:**
1. Approximate distance $\approx 46.49$ cm
2. Area under curve $= \frac{19}{3} \approx 6.33$
3. Identity proven
4. $x=4.5$, $y=2.5$
5. $x=1$ or $x=-\frac{1}{2}$
6. $x=\frac{4}{3}$ or $x=-1$
7a. $(r,\theta)=(5, -0.6435)$ radians
7b. $(-2.796, 4.145)$
8. $\int \frac{\ln x}{x} dx = \frac{(\ln x)^2}{2} + C$
9. Angle between vectors $\approx 45.57^\circ$
10. Identity proven