Question
Complete the square to find the vertex of this parabola. \( y^{2}-4 x-8 y-12=0 \) ([?], [ ])
Ask by Cruz Marshall. in the United States
Mar 09,2025
Upstudy AI Solution
Tutor-Verified Answer
Answer
The vertex of the parabola is at \((-7, 4)\).
Solution
We start with the equation
\[
y^{2} - 4x - 8y - 12 = 0.
\]
**Step 1. Isolate the terms involving \( y \):**
\[
y^{2} - 8y = 4x + 12.
\]
**Step 2. Complete the square for the \( y \)-terms.**
The expression \( y^{2} - 8y \) can be rewritten by completing the square. Recall that
\[
y^{2} - 8y = (y - 4)^{2} - 16.
\]
So, substitute back:
\[
(y - 4)^{2} - 16 = 4x + 12.
\]
**Step 3. Solve for \( x \):**
Add \( 16 \) to both sides:
\[
(y - 4)^{2} = 4x + 28.
\]
Now, solve for \( x \) by isolating it:
\[
4x = (y - 4)^{2} - 28,
\]
\[
x = \frac{1}{4}(y - 4)^{2} - 7.
\]
**Step 4. Identify the vertex.**
The equation is now in the form
\[
x = \frac{1}{4}(y - 4)^{2} - 7,
\]
which is the standard form of a sideways parabola \( x = a(y-k)^2 + h \) with vertex at \((h, k)\). Here, we have \( h = -7 \) and \( k = 4 \).
Thus, the vertex of the parabola is
\[
\boxed{(-7, \, 4)}.
\]
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Bonus Knowledge
To complete the square, we start with the equation \( y^{2} - 8y - 4x - 12 = 0 \). Rearranging gives us \( y^{2} - 8y = 4x + 12 \). Next, we add and subtract \( 16 \) (which is \((\frac{-8}{2})^2\)) to complete the square: \[ (y - 4)^{2} - 16 = 4x + 12. \] This simplifies to \( (y - 4)^{2} = 4x + 28 \), or \( (y - 4)^{2} = 4(x + 7) \). Now, we can see that the vertex of the parabola is at the point \((-7, 4)\). So the vertex is \([-7], [4]\).