Quadratic Function
**1. Stating the problem:**
We are given a quadratic function $$y=2x^2 - 3$$ and a partially filled table of values for $$x = -3, -2, -1, 0, 1, 2, 3$$ with corresponding $$y$$ values as $$15, 5, -1, -3, ???, 5, 15$$.
We need to:
(i) Find the value of $$y$$ when $$x=1$$.
(ii) Draw the graph of the function using the given scale.
(iii) Write the minimum value of the function.
(iv) Find the interval of $$x$$ values for which the function decreases or increases.
(v) Find the roots of the equation $$2x^2 -3 =0$$.
**2. Find the missing value $$y$$ for $$x=1$$:**
Substitute $$x=1$$ into the function:
$$y=2(1)^2 -3 = 2(1) - 3 = 2 - 3 = -1$$
So the missing value is $$-1$$.
**3. Graphing the function:**
- The function is $$y=2x^2 -3$$ which is a parabola opening upwards.
- Table of values now:
| x | -3 | -2 | -1 | 0 | 1 | 2 | 3 |
| y | 15 | 5 | -1 | -3 | -1 | 5 | 15 |
- Scale for x-axis: 10 small divisions = 1 unit.
- Scale for y-axis: 10 small divisions = 2 units.
- Plot the points and draw a smooth curve through them to form the parabola with vertex at (0, -3).
**4. Minimum value of the function:**
- The parabola opens upwards.
- The vertex is the minimum point.
- Vertex at $$x=0$$, $$y=-3$$.
Minimum value of $$y$$ is $$-3$$ at $$x=0$$.
**5. Intervals where the function increases or decreases:**
- Because the parabola opens upwards and is symmetric:
- It decreases on $$(-\infty, 0)$$.
- It increases on $$(0, +\infty)$$.
**6. Roots of the equation $$2x^2 - 3 = 0$$:**
Solve for $$x$$:
$$
2x^2 - 3 = 0
\Rightarrow 2x^2 = 3
\Rightarrow x^2 = \frac{3}{2}
\Rightarrow x = \pm \sqrt{\frac{3}{2}} = \pm \frac{\sqrt{6}}{2}
$$
**Final answers:**
(i) $$y = -1$$ at $$x=1$$.
(ii) The graph is a parabola opening upwards with vertex at $$(0, -3)$$.
(iii) Minimum value is $$-3$$ at $$x=0$$.
(iv) Decreasing on $$(-\infty, 0)$$, increasing on $$(0, +\infty)$$.
(v) Roots are $$x = \pm \frac{\sqrt{6}}{2}$$.