1. **State the problem:** Given the quadratic function $g(x) = 3x^2 - 8x + 2$,
(i) write $g(x)$ in the form $a(x+h)^2 + k$ (vertex form).
(ii) solve the equation $g(x) = 0$ and write the solutions correct to 2 decimal places.
2. **Formula and rules:**
To write a quadratic in vertex form, use completing the square:
$$g(x) = a(x+h)^2 + k$$
where $a$ is the coefficient of $x^2$, and $h,k$ are constants.
3. **Step (i) Completing the square:**
Start with
$$g(x) = 3x^2 - 8x + 2$$
Factor out 3 from the first two terms:
$$g(x) = 3\left(x^2 - \frac{8}{3}x\right) + 2$$
Complete the square inside the parentheses:
Take half of $-\frac{8}{3}$, which is $-\frac{4}{3}$, then square it:
$$\left(-\frac{4}{3}\right)^2 = \frac{16}{9}$$
Add and subtract $\frac{16}{9}$ inside the parentheses:
$$g(x) = 3\left(x^2 - \frac{8}{3}x + \frac{16}{9} - \frac{16}{9}\right) + 2$$
Group the perfect square trinomial:
$$g(x) = 3\left(\left(x - \frac{4}{3}\right)^2 - \frac{16}{9}\right) + 2$$
Distribute 3:
$$g(x) = 3\left(x - \frac{4}{3}\right)^2 - 3 \times \frac{16}{9} + 2$$
Simplify:
$$g(x) = 3\left(x - \frac{4}{3}\right)^2 - \frac{48}{9} + 2 = 3\left(x - \frac{4}{3}\right)^2 - \frac{16}{3} + 2$$
Convert 2 to thirds:
$$2 = \frac{6}{3}$$
So,
$$g(x) = 3\left(x - \frac{4}{3}\right)^2 - \frac{16}{3} + \frac{6}{3} = 3\left(x - \frac{4}{3}\right)^2 - \frac{10}{3}$$
4. **Answer for (i):**
$$g(x) = 3\left(x - \frac{4}{3}\right)^2 - \frac{10}{3}$$
5. **Step (ii) Solve $g(x) = 0$:**
Set the vertex form equal to zero:
$$3\left(x - \frac{4}{3}\right)^2 - \frac{10}{3} = 0$$
Add $\frac{10}{3}$ to both sides:
$$3\left(x - \frac{4}{3}\right)^2 = \frac{10}{3}$$
Divide both sides by 3:
$$\cancel{3}\left(x - \frac{4}{3}\right)^2 = \frac{10}{3} \div \cancel{3} = \frac{10}{9}$$
Take the square root of both sides:
$$x - \frac{4}{3} = \pm \sqrt{\frac{10}{9}} = \pm \frac{\sqrt{10}}{3}$$
Add $\frac{4}{3}$ to both sides:
$$x = \frac{4}{3} \pm \frac{\sqrt{10}}{3} = \frac{4 \pm \sqrt{10}}{3}$$
6. **Calculate decimal approximations:**
$$\sqrt{10} \approx 3.1623$$
So,
$$x_1 = \frac{4 + 3.1623}{3} = \frac{7.1623}{3} \approx 2.39$$
$$x_2 = \frac{4 - 3.1623}{3} = \frac{0.8377}{3} \approx 0.28$$
**Final answers:**
(i) $$g(x) = 3\left(x - \frac{4}{3}\right)^2 - \frac{10}{3}$$
(ii) $$x \approx 2.39 \text{ or } x \approx 0.28$$
Quadratic Vertex 7B9Cb9
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