Parabola Equation Fb973F
1. **Problem statement:** Find the equation of a parabola in standard form that passes through points $(-5, 2)$ and $(-2, 2)$ and has a maximum value of 20.
2. **Recall the standard form of a parabola:** $$y = a(x - h)^2 + k$$ where $(h, k)$ is the vertex.
3. Since the parabola has a maximum value of 20, the vertex is at $(h, k) = (h, 20)$ and the parabola opens downward, so $a < 0$.
4. The vertex lies midway between the points $(-5, 2)$ and $(-2, 2)$ because these points have the same $y$-value and are symmetric about the vertex.
Calculate the midpoint:
$$h = \frac{-5 + (-2)}{2} = \frac{-7}{2} = -3.5$$
So the vertex is at $(-3.5, 20)$.
5. Substitute the vertex into the standard form:
$$y = a(x + 3.5)^2 + 20$$
6. Use one of the given points to find $a$. Using $(-5, 2)$:
$$2 = a(-5 + 3.5)^2 + 20$$
$$2 = a(-1.5)^2 + 20$$
$$2 = a(2.25) + 20$$
7. Solve for $a$:
$$2 - 20 = 2.25a$$
$$-18 = 2.25a$$
$$a = \frac{-18}{2.25} = -8$$
8. Write the equation:
$$y = -8(x + 3.5)^2 + 20$$
9. Expand to standard form $y = ax^2 + bx + c$:
$$y = -8(x^2 + 7x + 12.25) + 20$$
$$y = -8x^2 - 56x - 98 + 20$$
$$y = -8x^2 - 56x - 78$$
10. **Domain and range:**
- Domain: All real numbers, $$(-\infty, \infty)$$
- Range: Since the parabola opens downward with maximum 20, range is $$(-\infty, 20]$$
**Final answer:**
$$y = -8x^2 - 56x - 78$$
Domain: $$(-\infty, \infty)$$
Range: $$(-\infty, 20]$$