Math Problem Statement

find the vertex, focus and directrix of (x+3)squared = -6(y-1)

Solution

The equation of the parabola is:

(x+3)2=6(y1)(x + 3)^2 = -6(y - 1)

This is a parabola that opens downwards because the coefficient of (y1)(y-1) is negative.

Step 1: Standard Form

The general form of a parabola that opens up or down is:

(xh)2=4p(yk)(x - h)^2 = 4p(y - k)

Here:

  • (h,k)(h, k) is the vertex.
  • pp is the distance from the vertex to the focus or to the directrix.

For our equation: (x+3)2=6(y1)(x + 3)^2 = -6(y - 1) We can rewrite it as: (x(3))2=4(32)(y1)(x - (-3))^2 = 4(-\frac{3}{2})(y - 1)

Thus:

  • h=3h = -3, k=1k = 1
  • 4p=6p=324p = -6 \Rightarrow p = -\frac{3}{2}

Step 2: Vertex

The vertex is: (3,1)\boxed{(-3, 1)}

Step 3: Focus

The focus is pp units away from the vertex along the axis of symmetry (the vertical line x=3x = -3). Since p=32p = -\frac{3}{2}, the focus is: Focus: (3,1+p)=(3,132)=(3,12)\text{Focus: } (-3, 1 + p) = (-3, 1 - \frac{3}{2}) = (-3, -\frac{1}{2})

Step 4: Directrix

The directrix is a horizontal line pp units away from the vertex in the opposite direction. The directrix is: Directrix: y=1p=1+32=52\text{Directrix: } y = 1 - p = 1 + \frac{3}{2} = \frac{5}{2}

Final Answer:

  1. Vertex: (3,1)(-3, 1)
  2. Focus: (3,12)(-3, -\frac{1}{2})
  3. Directrix: y=52y = \frac{5}{2}

Would you like a graph or further details?

Expanding Understanding:

  1. How can we verify the parabola’s direction from its equation?
  2. What changes if the parabola’s opening is horizontal?
  3. How do pp, focus, and directrix relate geometrically?
  4. Can you derive the equation if given the focus and directrix?
  5. What happens to the vertex if the equation shifts?

Tip:

The sign of 4p4p determines the direction of the parabola: positive for upwards/right and negative for downwards/left.

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Math Problem Analysis

Mathematical Concepts

Parabolas
Conic Sections
Coordinate Geometry

Formulas

Standard form of a parabola: (x-h)^2 = 4p(y-k)
Vertex formula: (h, k)
Focus formula: (h, k + p) for vertical parabolas
Directrix formula: y = k - p for vertical parabolas

Theorems

Geometric definition of a parabola

Suitable Grade Level

Grades 10-12