Writing the Equation of Parabolas
1. Determine which pattern to use (based on whether it is horizontal or vertical)
2. Substitute in h and k
3. Choose a coordinate to substitute in and solve for a.
4. Write your final equation with a, h, and k.
2. Substitute in h and k
3. Choose a coordinate to substitute in and solve for a.
4. Write your final equation with a, h, and k.
Remember the patterns:
Examples:
1. Find the equation of this parabola
This is a vertical parabola, so we are using the pattern
Our vertex is (5, 3), so we will substitute those numbers in for h and k:
Our vertex is (5, 3), so we will substitute those numbers in for h and k:
Now we must choose a point to substitute in. You can choose any point on the parabola except the vertex. Let's use (4, 5). We'll substitute 4 in for x and 5 for y.
Now we'll solve for a:
5 = a(1) + 3
2 = a
2 = a
To finish, we rewrite the pattern with h, k, and a:
2. Find the equation of the parabola:
This is a vertical parabola, so we are using the pattern
Our vertex is (-4, -1), so we will substitute those numbers in for h and k:
Our vertex is (-4, -1), so we will substitute those numbers in for h and k:
Now we must choose a point to substitute in. You can choose any point on the parabola except the vertex. Let's use (4, 3). We'll substitute 4 in for x and 3 for y.
Now we'll solve for a:
4 = a(16) - 4
8 = 16a
1/2 = a
To finish, we rewrite the pattern with h, k, and a:
8 = 16a
1/2 = a
To finish, we rewrite the pattern with h, k, and a:
Practice: Find the equation of these parabolas.
Answers: 1) 2) 3) 4) 5)
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