1. **Problem statement:**
We have a quadratic function $f$ with vertex at $(-2,-5)$ and y-intercept at point $P$. We need to find:
(a) The equation of the axis of symmetry.
(b) The values of $h$ and $k$ in the vertex form $f(x) = \frac{1}{4}(x-h)^2 + k$.
(c) The y-coordinate of $P$.
(d) The equation of line $L$ passing through $P$ with gradient $-1$.
(e) The distance between points $P$ and $Q$, where $Q$ is the second intersection of $L$ with the graph.
2. **Axis of symmetry:**
The axis of symmetry of a parabola in vertex form $f(x) = a(x-h)^2 + k$ is the vertical line $x = h$.
Since the vertex is at $(-2,-5)$, the axis of symmetry is:
$$x = -2$$
3. **Values of $h$ and $k$:**
From the vertex form $f(x) = \frac{1}{4}(x-h)^2 + k$, the vertex is at $(h,k)$.
Given vertex $(-2,-5)$, we have:
$$h = -2, \quad k = -5$$
4. **Y-coordinate of $P$ (y-intercept):**
The y-intercept occurs when $x=0$.
Substitute $x=0$ into $f(x)$:
$$f(0) = \frac{1}{4}(0 - (-2))^2 + (-5) = \frac{1}{4}(2)^2 - 5 = \frac{1}{4} \times 4 - 5 = 1 - 5 = -4$$
So, the y-coordinate of $P$ is $-4$.
5. **Equation of line $L$ passing through $P$ with gradient $-1$:**
Point $P$ is $(0,-4)$ and slope $m = -1$.
Using point-slope form:
$$y - y_1 = m(x - x_1)$$
$$y - (-4) = -1(x - 0)$$
$$y + 4 = -x$$
$$y = -x - 4$$
6. **Find point $Q$ where line $L$ intersects $f$ again:**
Set $f(x) = y$ and line $L$ equation equal:
$$\frac{1}{4}(x+2)^2 - 5 = -x - 4$$
Multiply both sides by 4 to clear fraction:
$$(x+2)^2 - 20 = -4x - 16$$
Expand $(x+2)^2 = x^2 + 4x + 4$:
$$x^2 + 4x + 4 - 20 = -4x - 16$$
Simplify left side:
$$x^2 + 4x - 16 = -4x - 16$$
Add $4x + 16$ to both sides:
$$x^2 + 4x - 16 + 4x + 16 = 0$$
$$x^2 + 8x = 0$$
Factor:
$$x(x + 8) = 0$$
Solutions:
$$x = 0 \quad \text{or} \quad x = -8$$
We already know $x=0$ corresponds to point $P$.
So, $Q$ is at $x = -8$.
Find $y$ coordinate of $Q$ using line $L$:
$$y = -(-8) - 4 = 8 - 4 = 4$$
So, $Q = (-8, 4)$.
7. **Distance between $P(0,-4)$ and $Q(-8,4)$:**
Use distance formula:
$$d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2} = \sqrt{(-8 - 0)^2 + (4 - (-4))^2} = \sqrt{(-8)^2 + (8)^2} = \sqrt{64 + 64} = \sqrt{128} = 8\sqrt{2}$$
**Final answers:**
(a) $x = -2$
(b) $h = -2$, $k = -5$
(c) $y$-coordinate of $P$ is $-4$
(d) Equation of line $L$: $y = -x - 4$
(e) Distance between $P$ and $Q$ is $8\sqrt{2}$
Quadratic Vertex 36648B
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