1. **State the problem:** Find the equation of a parabola whose axis is parallel to the x-axis and passes through points (3, 1), (0, 0), and (8, -4).
2. **Recall the form of the parabola:** Since the axis is parallel to the x-axis, the parabola can be expressed as $$ (y - k)^2 = 4p(x - h) $$ where $(h, k)$ is the vertex.
3. **Use the general form:** We can rewrite the equation as $$ y^2 + Ay + Bx + C = 0 $$ or better, express $x$ in terms of $y$ as $$ x = a y^2 + b y + c $$ because the axis is horizontal.
4. **Set up equations using the points:** Substitute each point $(x, y)$ into $$ x = a y^2 + b y + c $$
For (3, 1): $$ 3 = a(1)^2 + b(1) + c = a + b + c $$
For (0, 0): $$ 0 = a(0)^2 + b(0) + c = c $$
For (8, -4): $$ 8 = a(-4)^2 + b(-4) + c = 16a - 4b + c $$
5. **From the second equation:** $$ c = 0 $$
6. **Rewrite the other equations:**
From (3,1): $$ 3 = a + b + 0 = a + b $$
From (8,-4): $$ 8 = 16a - 4b + 0 = 16a - 4b $$
7. **Solve the system:**
From $$ a + b = 3 $$, we get $$ b = 3 - a $$
Substitute into the second:
$$ 8 = 16a - 4(3 - a) = 16a - 12 + 4a = 20a - 12 $$
Add 12 to both sides:
$$ 8 + 12 = 20a $$
$$ 20 = 20a $$
Divide both sides by 20:
$$ \cancel{20} = \cancel{20}a $$
$$ 1 = a $$
8. **Find b:**
$$ b = 3 - a = 3 - 1 = 2 $$
9. **Write the equation:**
$$ x = y^2 + 2y $$
or equivalently,
$$ x = y^2 + 2y + 0 $$
10. **Final answer:** The equation of the parabola is $$ \boxed{x = y^2 + 2y} $$
Parabola Horizontal Axis 13879B
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