Math  /  Geometry

QuestionGiven the general form of an ellipse, 4x2+y224x+8y+16=04 x^{2}+y^{2}-24 x+8 y+16=0, determine the correct value for each characteristic.
Orientation: [ Select ]
Center (h,k)(h, k) : h=h= [Select ] k=k= [ Select ]
Length of the major axis: [ Select ]

Studdy Solution

STEP 1

What is this asking? We're given an equation for an ellipse and need to find its orientation, center, and the length of its major axis! Watch out! Don't mix up the major and minor axes – the major axis is the longer one!
Also, remember that completing the square involves adding the *same* value to both sides of the equation.

STEP 2

1. Rewrite the equation
2. Complete the square
3. Analyze the ellipse

STEP 3

Let's **group** the xx terms and yy terms together to make completing the square easier!
We'll rewrite the given equation, 4x2+y224x+8y+16=04x^2 + y^2 - 24x + 8y + 16 = 0, as 4(x26x)+(y2+8y)=164(x^2 - 6x) + (y^2 + 8y) = -16.
See how we factored out the coefficient of the squared terms?
This sets us up perfectly for the next step!

STEP 4

Now, let's **complete the square** for the xx terms.
Take half of the coefficient of the xx term, which is 62=3\frac{-6}{2} = -3, square it to get (3)2=9(-3)^2 = 9, and add it *inside* the parentheses.
Remember, since we factored out a **4**, we're actually adding 49=364 \cdot 9 = 36 to the left side, so we must add **36** to the right side as well!
This keeps our equation balanced!

STEP 5

Our equation now looks like 4(x26x+9)+(y2+8y)=16+364(x^2 - 6x + 9) + (y^2 + 8y) = -16 + 36.
Let's do the same for the yy terms!
Half of the coefficient of the yy term is 82=4\frac{8}{2} = 4, and squaring it gives us 42=164^2 = 16.
Adding **16** to both sides, we get 4(x26x+9)+(y2+8y+16)=16+36+164(x^2 - 6x + 9) + (y^2 + 8y + 16) = -16 + 36 + 16.

STEP 6

Now we can rewrite our equation in a much nicer form: 4(x3)2+(y+4)2=364(x-3)^2 + (y+4)^2 = 36.
Almost there!
To get the standard form of an ellipse equation, we need a **1** on the right side.

STEP 7

Let's **divide** both sides of the equation by 36 to achieve this.
We get 4(x3)236+(y+4)236=3636\frac{4(x-3)^2}{36} + \frac{(y+4)^2}{36} = \frac{36}{36}, which simplifies to (x3)29+(y+4)236=1\frac{(x-3)^2}{9} + \frac{(y+4)^2}{36} = 1.
This is the standard form of an ellipse equation!

STEP 8

From the standard form, (xh)2a2+(yk)2b2=1\frac{(x-h)^2}{a^2} + \frac{(y-k)^2}{b^2} = 1, we can see that the center of our ellipse is (h,k)=(3,4)(h, k) = (3, -4).
Since 36>936 > 9, the major axis is vertical (along the yy-axis).

STEP 9

The length of the major axis is 2b2b, where b2=36b^2 = 36, so b=6b = 6.
Therefore, the length of the major axis is 26=122 \cdot 6 = 12.

STEP 10

Orientation: Vertical Center (h,k)(h, k): h=3h = 3, k=4k = -4 Length of the major axis: 12

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