Identify the line of symmetry of the parabola defined by
y = -2(x + 4)^2 + 6

x=6
x= -4
x= -6
x=4

Question

Identify the line of symmetry of the parabola defined by
y = -2(x + 4)^2 + 6

x=6
x= -4
x= -6
x=4

directrix · Answer

Do you know the x-coordinate of the vertex of the parabola?

beccab003 · Answer

It's -6?

anonymous · Answer

do you know the equation to find the axis of symmetry?

beccab003 · Answer

No

anonymous · Answer

$$x=\frac{-b }{2a }$$

directrix · Answer

@BeccaB003

What value of x makes (x + 4) equal to 0?

beccab003 · Answer

-4

directrix · Answer

Yes, so x = -4 is the equation of the axis of symmetry. Look at the attached graph.

directrix · Answer

@BeccaB003

beccab003 · Answer

Yes, I'm here. I was looking at what you said. So I don't need to worry about the other parts of the equation as long as (x+4)=0?

directrix · Answer

First up, did you see the graph?

beccab003 · Answer

yes

anonymous · Answer

@Directrix will you please help me after?

directrix · Answer

The graph gives it away.

To answer your question, when the parabola's equation is written in this type form:  y = -2(x + 4)^2 + 6, you can pick off the coordinates of the vertex.

In this form x + 4 the x coordinate of the vertex is whatever makes x+4 = 0.
For this task of finding the axis of symmetry, the other terms are not necessary when the equation is written in this form.

beccab003 · Answer

okay. Thanks for helping me understand better. You are most helpful. :)

directrix · Answer

See attachment. That form is called the vertex form of a parabola. Read more here: http://www.mathwarehouse.com/geometry/parabola/standard-and-vertex-form.php

beccab003 · Answer

Thanks!

directrix · Answer

You are welcome.