Vertex Form of Quadratic Equation (2025)

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 (2025)

FAQs

How to get the vertex form of a 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 many answers should a quadratic equation have? ›

Solving the quadratic equation. A quadratic equation with real or complex coefficients has two solutions, called roots. These two solutions may or may not be distinct, and they may or may not be real.

What does the vertex form of a parabola tell you? ›

In Mathematics, the vertex formula helps to find the vertex coordinate of a parabola, when the graph crosses its axes of symmetry. Generally, the vertex point is represented by (h, k). We know that the standard equation of a parabola is y=ax2+bx+c.

How do you pass 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.

Is a slope in vertex form? ›

Algebraically speaking, vertex form applies to quadratic equations, and it is the equation y = a(x - h)2 + k, where (h,k) is the vertex of the parabola. Slope-intercept form applies to linear equations, and it is the equation y = mx + b, where m is the slope of the line, and b is the y-intercept of the line.

How to turn factored form into vertex form? ›

To find the vertex from factored form, you must first expand the equation into standard form. From there, you must complete the square (see above!). If you are following my example of factored form, you should get x^2+2x-8 once you expand. From there, you can convert that to vertex form, which will be (x+1)^2 - 9.

Does the quadratic formula give 2 answers? ›

As we have seen, there can be 0, 1, or 2 solutions to a quadratic equation, depending on whether the expression inside the square root sign, (b2 - 4ac), is positive, negative, or zero. This expression has a special name: the discriminant.

Are there always two answers to a quadratic equation? ›

There are commonly two solutions to quadratic equations because the solutions are where the parabola crosses the -axis. If the vertex is below the -axis and the parabola opens up, the graph will cross twice, and if the vertex is above the -axis and the parabola opens down, the graph will, again, cross twice.

Can a quadratic have one answer? ›

Explanation: The solution of a quadratic equation ax2 + bx + c = 0 is given by the quadratic formula x = [-b ± √(b2 - 4ac)] / 2a, to find the solution of a quadratic equation. In the case of one real solution, the value of discriminant b2 - 4ac is zero. For example, x2 + 2x + 1 = 0 has only one solution x = -1.

How is the vertex formula derived? ›

How is the Vertex Formula Derived? The Vertex Formula is derived from the completion of the square method applied to the standard parabolic equation y = ax^2 + bx + c. This process leads to the vertex form y = a(x - h)^2 + k, where h = -b / (2a) and k = - (b^2 - 4ac) / (4a).

How to find zeros from vertex form? ›

In order to find the zeroes, you must put the value of f(x) to zero and solve for both values of x. Now, take the average of the zeroes. This means that the x value of the vertex is equal to 1/2. Substitute the value of x into the equation.

What is an example of a vertex? ›

A common way to describe them would be corners. For example, a square has four vertices, or corners, since there are four places where the sides connect to each other. A triangle has three vertices. The more sides a shape has, the more vertices it also has.

What is the easiest way to find vertex form? ›

Finding the vertex of the quadratic by using the equation x=-b/2a, and then substituting that answer for y in the orginal equation. Then, substitute the vertex into the vertex form equation, y=a(x-h)^2+k. (a will stay the same, h is x, and k is y).

How do you find the vertex given the quadratic equation 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.

What does k do 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).

How to convert quadratic equation to standard form? ›

The process of converting the vertex form of a quadratic equation into the standard form is pretty simple and it is done by simply evaluating (x - h)2 = (x - h) (x - h) and simplifying.

References

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