Looking at the worksheet, there are four problems to solve:
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Problem 1:
Write equation in standard form (if not already), then graph and label vertex, axis of symmetry, direction of opening, focus, and directrix.
Equation given:
y = x² + 5
This is already in standard form for a vertical parabola: y = ax² + bx + c → here, a=1, b=0, c=5.
Vertex: For y = ax² + bx + c, vertex x-coordinate = -b/(2a) = 0/2 = 0 → y = 0² + 5 = 5 → Vertex:
(0, 5)
Axis of symmetry: x = 0 (the y-axis)
Direction of opening: Since a = 1 > 0 → opens
upward
Focus and Directrix:
For vertical parabola y = a(x-h)² + k, the distance from vertex to focus is p = 1/(4a)
Here, a = 1 → p = 1/4
Since it opens upward:
- Focus: (h, k + p) = (0, 5 + 0.25) =
(0, 5.25)
- Directrix: y = k - p = 5 - 0.25 =
y = 4.75
Graph: Plot vertex at (0,5), draw symmetric curve opening up through points like (-1,6), (1,6), etc. Draw dashed line x=0 (axis), mark focus at (0,5.25), draw directrix as horizontal dashed line at y=4.75.
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Problem 2:
Equation:
x = 2(y + 3)² - 1
This is a horizontal parabola (x in terms of y). Standard form: x = a(y-k)² + h
Here, a = 2, k = -3, h = -1
Vertex:
(h, k) = (-1, -3)
Axis of symmetry: y = k →
y = -3
Direction of opening: a = 2 > 0 → opens
right
p = 1/(4a) = 1/(8) = 0.125
Since it opens right:
- Focus: (h + p, k) = (-1 + 0.125, -3) =
(-0.875, -3)
- Directrix: x = h - p = -1 - 0.125 =
x = -1.125
Graph: Plot vertex at (-1,-3), open right, symmetric over y=-3. Mark focus slightly right of vertex, draw directrix as vertical dashed line left of vertex.
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Problem 3:
Given: vertex (2, 3), focus (5, 3)
Same y-coordinate → horizontal parabola (opens left or right)
Distance from vertex to focus: |5 - 2| = 3 → so p = 3
Since focus is to the right of vertex → opens
right
Standard form for horizontal parabola: x = a(y - k)² + h
We know h=2, k=3, and p = 1/(4a) → 3 = 1/(4a) → 4a = 1/3 → a = 1/12
So equation:
x = (1/12)(y - 3)² + 2
Directrix: x = h - p = 2 - 3 =
x = -1
Graph: Vertex at (2,3), opens right, directrix at x=-1, focus at (5,3).
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Problem 4:
Given: vertex (9, -2), directrix x = 3
Directrix is vertical → parabola opens horizontally.
Vertex x = 9, directrix x = 3 → distance between them = |9 - 3| = 6 → so p = 6
Since directrix is to the left of vertex, parabola opens
right
Again, use x = a(y - k)² + h
h = 9, k = -2
p = 1/(4a) → 6 = 1/(4a) → 4a = 1/6 → a = 1/24
Equation:
x = (1/24)(y + 2)² + 9
Focus: Since opens right, focus is at (h + p, k) = (9 + 6, -2) =
(15, -2)
Graph: Vertex at (9,-2), opens right, directrix at x=3, focus at (15,-2).
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Final Answer:
1. Equation: y = x² + 5; Vertex: (0,5); Axis: x=0; Opens: Up; Focus: (0, 5.25); Directrix: y=4.75
2. Equation: x = 2(y+3)² - 1; Vertex: (-1,-3); Axis: y=-3; Opens: Right; Focus: (-0.875, -3); Directrix: x=-1.125
3. Equation: x = (1/12)(y - 3)² + 2; Directrix: x = -1
4. Equation: x = (1/24)(y + 2)² + 9; Focus: (15, -2)
Parent Tip: Review the logic above to help your child master the concept of algebra 2 parabolas worksheet.