Vertex Form of Quadratic Equation (2024)

Vertex Form of Quadratic Equation (1)

Vertex Form of Quadratic Functions
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Vertex Form of Quadratic Equation (2)

FYI: Different textbooks have different interpretations of the reference "standard form" of a quadratic function. Some say f (x) = ax2 + bx + c is "standard form", while others say that f (x) = a(x - h)2 + k is "standard form". To avoid confusion, this site will not refer to either as "standard form", but will reference f (x) = a(x - h)2 + k as "vertex form" and will reference f (x) = ax2 + bx + c by its full statement.


Vertex Form of Quadratic Equation (3)

The vertex form of a quadratic function is given by
f (x) = a(x - h)2 + k, where (h, k) is the vertex of the parabola.

Remember: the "vertex? is the "turning point".

When written in "vertex form":
(h, k) is the vertex of the parabola, and x = h is the axis of symmetry.

• the h represents a horizontal shift (how far left, or right, the graph has shifted from x = 0).

• the k represents a vertical shift (how far up, or down, the graph has shifted from y = 0).

• notice that the h value is subtracted in this form, and that the k value is added.
If the equation is y = 2(x - 1)2 + 5, the value of h is 1, and k is 5.
If the equation is y = 3(x + 4)2 - 6, the value of h is -4, and k is -6.

Vertex Form of Quadratic Equation (4)


Vertex Form of Quadratic Equation (5) To Convert from f (x) = ax2 + bx + c Form to Vertex Form:
Method 1: Completing the Square
To convert a quadratic from y = ax2 + bx + c form to vertex form, y = a(x - h)2+ k, you use the process of completing the square. Let's see an example.

Vertex Form of Quadratic Equation (6) Convert y = 2x2 - 4x + 5 into vertex form, and state the vertex.

Equation in y = ax2 + bx + c form.

y = 2x2 - 4x + 5

Since we will be "completing the square" we will isolate the x2 and x terms ... so move the + 5 to the other side of the equal sign.

y - 5 = 2x2 - 4x

We need a leading coefficient of 1 for completing the square ... so factor out the current leading coefficient of 2.

y - 5 = 2(x2 - 2x)

Get ready to create a perfect square trinomial. BUT be careful!! In previous completing the square problems with a leading coefficient not 1, our equations were set equal to 0. Now, we have to deal with an additional variable, "y" ... so we cannot "get rid of " the factored 2. When we add a box to both sides, the box will be multiplied by 2 on both sides of the equal sign.

Vertex Form of Quadratic Equation (7)

Find the perfect square trinomial. Take half of the coefficient of the x-term inside the parentheses, square it, and place it in the box.

Vertex Form of Quadratic Equation (8)

Simplify and convert the right side to a squared expression.

y - 3 = 2(x - 1)2

Isolate the y-term ... so move the -3 to the other side of the equal sign.

y = 2(x - 1)2 + 3

In some cases, you may need to transform the equation into the "exact" vertex form of
y
= a(x - h)2 + k, showing a "subtraction" sign in the parentheses before the h term, and the "addition" of the k term. (This was not needed in this problem.)

y = 2(x - 1)2 + 3
Vertex form of the equation.
Vertex = (h, k) = (1, 3)

(The vertex of this graph will be moved one unit to the right and three units up from (0,0), the vertex of its parent y = x2.)


Here's a sneaky, quick tidbit:

Vertex Form of Quadratic Equation (9)

When working with the vertex form of a quadratic function,
Vertex Form of Quadratic Equation (10) and Vertex Form of Quadratic Equation (11).
The "a" and "b" referenced here refer to f (x) = ax2 + bx + c.

Method 2: Using the "sneaky tidbit", seen above, to convert to vertex form:

y = ax2 + bx + c form of the equation.

y = 2x2 - 4x + 5

Find the vertex, (h, k).
Vertex Form of Quadratic Equation (12) and Vertex Form of Quadratic Equation (13).
[f (h) means to plug your answer for h into the original equation for x.]

a = 2 and b = -4
Vertex Form of Quadratic Equation (14)
Vertex Form of Quadratic Equation (15)
Vertex: (1,3)

Write the vertex form.
y = a(x - h)2 + k

y = 2(x - 1)2 + 3


Vertex Form of Quadratic Equation (16)

Vertex Form of Quadratic Equation (17) To Convert from Vertex Form to y = ax2 + bx + c Form:

Simply multiply out and combine like terms:

y = 2(x - 1)2 + 3
y = 2(x2 - 2x + 1) + 3
y = 2x2 - 4x + 2 + 3
y = 2x2 - 4x + 5

Vertex Form of Quadratic Equation (18)

Vertex Form of Quadratic Equation (19) Graphing a Quadratic Function in Vertex Form:

1. Start with the function in vertex form:
y = a(x - h)2 + k

y = 3(x - 2)2 - 4

2. Pull out the values for h and k.
If necessary, rewrite the function so you can clearly see the h and k values.
(h, k) is the vertex of the parabola.
Plot the vertex.

y = 3(x - 2)2 + (-4)

h = 2; k = -4
Vertex: (2, -4)

3. The line x = h is the axis of symmetry.
Draw the axis of symmetry.

x = 2 is the axis of symmetry

4. Find two or three points on one side of the axis of symmetry, by substituting your chosen x-values into the equation.

For this problem, we chose (to the left of the axis of symmetry):

x = 1; y = 3(1 - 2)2 - 4 = -1

x = 0; y = 3(0 - 2)2 - 4 = 8

Plot (1, -1) and (0,8)

Vertex Form of Quadratic Equation (20)

5. Plot the mirror images of these points across the axis of symmetry, or plot new points on the right side.
Draw the parabola.
Remember, when drawing the parabola to avoid "connecting the dots" with straight line segments. A parabola is curved, not straight, as its slope is not constant.

Vertex Form of Quadratic Equation (21)

Vertex Form of Quadratic Equation (22)

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Vertex Form of Quadratic Equation (2024)

FAQs

Vertex Form of Quadratic Equation? ›

The vertex form of a quadratic function is f(x) = a(x – h)2 + k, where a, h, and k are constants. of the parabola is at (h, k). When the quadratic parent function f(x) = x2 is written in vertex form, y = a(x – h)2 + k, a = 1, h = 0, and k = 0.

How to find the vertex of a quadratic equation? ›

We find the vertex of a quadratic equation with the following steps:
  1. Get the equation in the form y = ax2 + bx + c.
  2. Calculate -b / 2a. This is the x-coordinate of the vertex.
  3. To find the y-coordinate of the vertex, simply plug the value of -b / 2a into the equation for x and solve for y.

How to convert quadratic equation to vertex form? ›

How Do You Convert Standard Form to Vertex Form? To convert standard form to vertex form, Convert y = ax2 + bx + c into the form y = a (x - h)2 + k by completing the square. Then y = a (x - h)2 + k is the vertex form.

What is the vertex of a parabola? ›

The vertex of a parabola is the point where the parabola crosses its axis of symmetry.

How to find zeros from vertex form? ›

Once you have it in vertex form you should have something like (x - h)^2 + k = 0 (since zeros are where f(x) = 0), so you solve from farthest from x to closest, so subtract k, (x-h)^2 = -k, take square root, so x - h = ± √-k, and finally add h, so x = h ± √-k.

What is the vertex form of a quadratic equation example? ›

Vertex of a Quadratic Function

Specifically, we can use y = 3x2 + 6x + 1 as an example. Notice that the point at (-1,-2) is the lowest point on the graph. This is what we call the vertex. We can also find the coordinates of the vertex from the equation itself, using this formula: x = -b/2a.

Is there a formula for vertex? ›

The vertex form of the parabola y = a(x - h)2 + k. There are two ways in which we can determine the vertex(h, k). They are: (h, k) = (-b/2a, -D/4a), where D(discriminant) = b2 - 4ac.

How to find the a in vertex form? ›

y=a(x−h)^2+k Where (h,k) is the max or min.
  1. Look at the graph.
  2. Find the vertex of the graph (h,k)
  3. Vertex is the highest / lowest point of the graph known as Max or min (h,K) ...
  4. To find the "a " ----> pick a point on the graph other than vertex. ( ...
  5. plug it into the vertex form and slove for "a"
Sep 20, 2013

What is an example of a vertex? ›

Find places where two lines or edges come together, like the corner of a desk, the points on a picture frame, the corners on a tissue box. These are examples of vertices. A vertex, first of all, is the singular form of 'vertices', and it represents the location where two or more lines or edges are connected.

What is the vertex and zeros of a quadratic function? ›

All quadratic functions have a vertex and many cross the x axis at points called zeros or roots. If we know the vertex and its zeros, quadratic functions become very easy to draw since the vertex is also a line of symmetry (the zeros are equidistant from the vertex on either side).

Do you use the quadratic formula to find the zeros? ›

*Given a function of the form f(x)=ax2+bx+c , one can find the zeroes of the function (that is, where f(x)=0 ) by using the quadratic formula: x=−b±√b2−4ac2a .

What is the formula for the vertices of a quadratic equation? ›

The vertex formula is used to find the vertex of a parabola. The formula to find the vertex is (h, k) = (-b/2a, -D/4a), where D = b2-4ac.

How to find the vertex of a quadratic function in intercept form? ›

Intercept Form of a Quadratic Function

Because of symmetry, the axis of symmetry is halfway between the x-intercepts. The vertex is on the axis of symmetry, so it can be found by substituting the x-coordinate of the axis of symmetry into the original function to find the y-value.

How to find the vertex of a function with absolute value? ›

The vertex of the absolute value equation f(x) = a |x - h| + k is given by (h, k). We can also find the vertex of f(x) = a |x - h| + k using the formula (x - h) = 0. On determining the value of x, we substitute the value into the equation to find the value of k.

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