1. **Solve for exact solutions of** $\frac{1}{x} = 2x + 3$.
Multiply both sides by $x$ (assuming $x \neq 0$):
$$1 = 2x^2 + 3x$$
Rewrite as a quadratic equation:
$$2x^2 + 3x - 1 = 0$$
2. **Use quadratic formula:**
$$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$
with $a=2$, $b=3$, and $c=-1$.
Calculate discriminant:
$$\Delta = 3^2 - 4 \times 2 \times (-1) = 9 + 8 = 17$$
3. **Find roots:**
$$x = \frac{-3 \pm \sqrt{17}}{4}$$
Hence, exact solutions are
$$x = \frac{-3 + \sqrt{17}}{4}$$ and $$x = \frac{-3 - \sqrt{17}}{4}$$.
4. **Show $f(x) = x^2 - 4x + 9$ is positive for all $x$:**
Complete the square:
$$f(x) = x^2 - 4x + 9 = (x^2 -4x + 4) + 5 = (x - 2)^2 + 5$$
Since $(x - 2)^2 \geq 0$ for all $x$, and 5 > 0, $f(x) > 0$ for all real $x$.
5. **Minimum point of $f(x)$:**
The vertex of a parabola $y = a(x-h)^2 + k$ is at $(h,k)$. Here,
$$h = 2, k = 5$$
Minimum point coordinates:
$$(2,5)$$.
6. **Sketch graph of $f(x)$ includes intercepts & line of symmetry:**
- **Line of symmetry:** $x = 2$.
- **$y$-intercept at $x=0$: $$f(0) = 0^2 - 4(0) + 9 = 9$$ so point $(0,9)$.
- **Check for $x$-intercepts:** Solve $x^2 - 4x + 9 = 0$, discriminant is $16 - 36 = -20 < 0$, so no real roots.
7. **Find intersection points of**
$$y_1 = x^2 - 4x + 2$$ and $$y_2 = -x^2 - 8x$$
Set equal:
$$x^2 - 4x + 2 = -x^2 - 8x$$
$$x^2 + x^2 - 4x + 8x + 2 = 0$$
$$2x^2 + 4x + 2 = 0$$
Divide all terms by 2:
$$x^2 + 2x + 1 = 0$$
$$(x + 1)^2 = 0$$
So single solution: $x=-1$.
Find $y$ coordinate:
$$y = (-1)^2 -4(-1) + 2 = 1 + 4 + 2 = 7$$
Intersection point: $(-1, 7)$.
8. **Sketch graph of**
$$f(x) = e^{2x} + 2$$
- This is an exponential curve shifted up by 2.
- **Horizontal asymptote:** $y = 2$.
- The graph increases rapidly as $x$ grows.
9. **Given** $y = \log_2 x$,
(a) Express $$\log_2 x^2$$ in terms of $y$:
Using log power rule:
$$\log_2 x^2 = 2 \log_2 x = 2y$$.
(b) The asymptote of $y= \log_2 x$ is the vertical line where the function is undefined:
$$x = 0$$.
**Final answers:**
a) $$x = \frac{-3 \pm \sqrt{17}}{4}$$
b)i) $f(x)$ is positive $orall x\in \mathbb{R}$.
ii) Min point: $(2,5)$.
iii) Graph described above.
c) Intersection point: $(-1,7)$.
2) Sketch described, asymptote $y=2$.
3) a) $\log_2 x^2 = 2y$; b) asymptote: $x=0$.
Functions Assignment
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