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 axis of symmetry,
(b) values of $h$ and $k$ in $f(x)=\frac{1}{4}(x-h)^2+k$,
(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 $L$ and $f$.
2. **Axis of symmetry:**
The axis of symmetry of a parabola with vertex $(h,k)$ is the vertical line $x=h$.
Since vertex is $(-2,-5)$, axis of symmetry is:
$$x=-2$$
3. **Values of $h$ and $k$:**
Given $f(x)=\frac{1}{4}(x-h)^2+k$ and vertex $(h,k)=(-2,-5)$, so:
$$h=-2, \quad k=-5$$
4. **Y-coordinate of $P$ (y-intercept):**
The y-intercept occurs at $x=0$, so:
$$f(0)=\frac{1}{4}(0+2)^2 -5 = \frac{1}{4}(2)^2 -5 = \frac{1}{4} \times 4 -5 = 1 -5 = -4$$
So, $P=(0,-4)$.
5. **Equation of line $L$ with gradient $-1$ passing through $P(0,-4)$:**
Using point-slope form:
$$y - y_1 = m(x - x_1)$$
$$y + 4 = -1(x - 0)$$
$$y = -x - 4$$
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:
$$(x+2)^2 - 20 = -4x -16$$
Expand:
$$x^2 + 4x + 4 - 20 = -4x -16$$
Simplify left:
$$x^2 + 4x -16 = -4x -16$$
Bring all terms to one side:
$$x^2 + 4x -16 + 4x +16 = 0$$
$$x^2 + 8x = 0$$
Factor:
$$x(x + 8) = 0$$
Solutions:
$$x=0 \quad \text{or} \quad x=-8$$
$x=0$ 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) Axis of symmetry: $x=-2$
(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 63Cb77
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