Math Problem Statement

Match the standard form of the conic section to its type (circle or ellipse) and write the equation of the ellipse using the provided vertices and foci.

Solution

Let's solve these questions step by step.


1. Matching the standard form of the conic section

To determine the type of conic section, we analyze each equation:

  1. Equation 1: 4x2+9y2+40x36y8=04x^2 + 9y^2 + 40x - 36y - 8 = 0

    • The coefficients of x2x^2 and y2y^2 are positive but different (44 and 99), which indicates this is an ellipse.
    • Match this to B. Ellipse.
  2. Equation 2: 4x7y+23=104x - 7y + 23 = 10

    • Simplify: 4x7y+13=04x - 7y + 13 = 0.
    • There are no squared terms (x2x^2 or y2y^2). This is a linear equation and therefore not a conic.
    • Match this to C. Not a Conic.
  3. Equation 3: x2+y24x18y+49=0x^2 + y^2 - 4x - 18y + 49 = 0

    • Rearrange terms to complete the square:
      x24x+y218y+49=0x^2 - 4x + y^2 - 18y + 49 = 0.
      Completing the square for xx and yy:
      • x24x=(x2)24x^2 - 4x = (x-2)^2 - 4,
      • y218y=(y9)281y^2 - 18y = (y-9)^2 - 81.
        Substituting back:
        (x2)24+(y9)281+49=0    (x2)2+(y9)2=36.(x-2)^2 - 4 + (y-9)^2 - 81 + 49 = 0 \implies (x-2)^2 + (y-9)^2 = 36.
        This is a circle with center (2,9)(2, 9) and radius 66.
      • Match this to A. Circle.

Final Matching:

  1. B. Ellipse
  2. C. Not a Conic
  3. A. Circle

2. Writing the equation of the ellipse

Vertices: (1,4)(-1, 4) and (1,6)(-1, -6)
Foci: (1,3)(-1, 3) and (1,5)(-1, -5)

Step 1: Center of the ellipse
The center lies midway between the vertices.
Center=(1,4+(6)2)=(1,1).\text{Center} = \left( -1, \frac{4 + (-6)}{2} \right) = (-1, -1).

Step 2: Distance between vertices (major axis length)
The distance between the vertices is:
4(6)=10.|4 - (-6)| = 10.
Thus, the semi-major axis length is:
a=102=5.a = \frac{10}{2} = 5.

Step 3: Distance between foci
The distance between the foci is:
3(5)=8.|3 - (-5)| = 8.
Thus, the distance from the center to a focus (c) is:
c=82=4.c = \frac{8}{2} = 4.

Step 4: Semi-minor axis length (bb)
Using the ellipse relation a2=b2+c2a^2 = b^2 + c^2:
52=b2+42    25=b2+16    b2=9    b=3.5^2 = b^2 + 4^2 \implies 25 = b^2 + 16 \implies b^2 = 9 \implies b = 3.

Step 5: Equation of the ellipse
The major axis is vertical (aligned along yy) because the vertices have the same xx-coordinate. Therefore, the equation is:
(x+1)2b2+(y+1)2a2=1.\frac{(x+1)^2}{b^2} + \frac{(y+1)^2}{a^2} = 1.
Substitute a2=25a^2 = 25 and b2=9b^2 = 9:
(x+1)29+(y+1)225=1.\frac{(x+1)^2}{9} + \frac{(y+1)^2}{25} = 1.

Correct Answer:
(x+1)29+(y+1)225=1.\frac{(x+1)^2}{9} + \frac{(y+1)^2}{25} = 1.


Final Results:

  1. Matching the Conic Sections:

    • 1: B. Ellipse
    • 2: C. Not a Conic
    • 3: A. Circle
  2. Equation of the Ellipse:
    (x+1)29+(y+1)225=1.\frac{(x+1)^2}{9} + \frac{(y+1)^2}{25} = 1.


Follow-Up Questions:

  1. How do you complete the square for conic equations?
  2. What is the general form of an ellipse centered at (h,k)(h, k)?
  3. How do you determine the major and minor axes of an ellipse?
  4. What distinguishes a circle from an ellipse mathematically?
  5. How do you identify whether an equation represents a conic section?

Tip:

To identify conic sections, focus on the coefficients of x2x^2 and y2y^2. If they are equal and positive, it's a circle; if they differ but have the same sign, it's an ellipse.

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Math Problem Analysis

Mathematical Concepts

Conic Sections
Ellipses
Completing the Square
Standard Equation of Ellipse

Formulas

Ellipse equation: (x-h)^2/a^2 + (y-k)^2/b^2 = 1
Distance formula: sqrt((x2-x1)^2 + (y2-y1)^2)
Relation for ellipse axes: a^2 = b^2 + c^2

Theorems

Properties of Ellipses
Completing the Square for Quadratic Forms

Suitable Grade Level

Grades 10-12