Vertex Formula - What is Vertex Formula? Examples (2024)

The Vertex formula of a parabola is used to find the coordinates of the point where the parabola crosses its axis of symmetry. The vertex is the point (h,k). As we know the standard equation of a parabola is y = ax2+bx+c.If the coefficient x2 is positive then the vertex is the bottom of the U- shaped curve and if it is negative the vertex point is the top of the U-shaped curve. The vertex at which the parabola is minimum (when the parabola opens up) or maximum (when the parabola opens down) and the parabola turns (or) changes its direction. Let's learn more about the vertex formula and solve examples.

What is Vertex Formula?

The vertex formula helps to find the vertex coordinates of a parabola. The standard form of a parabola is y = ax2 + bx + c. 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:

  1. (h, k) = (-b/2a, -D/4a), where D(discriminant) = b2 - 4ac
  2. (h,k), where h = -b / 2a and evaluate y at h to find k.

Vertex Formula

The two vertex formulas to find the vertex is:

Formula 1: (h, k) = (-b/2a, -D/4a)

where,

  • D is the denominator
  • h,k are the coordinates of the vertex

Formula 2: x-coordinate of the vertex = -b / 2a

Derivation of Vertex Formulas

Formula 1

We know that the standard form of a parabola is, y = ax2 + bx + c. Let us convert it to the vertex form y = a(x - h)2 + k by completing the squares.

Subtracting c from both sides:

y - c = ax2 + bx

Taking "a" as the common factor:

y - c = a (x2 + b/a x)

Here, half the coefficient of x is b/2a and its square is b2/4a2. Adding and subtracting this on the right side (inside the parentheses):

y - c = a (x2 + b/a x + b2/4a2 - b2/4a2)

We can write x2 + b/a x + b2/4a2 as (x + b/2a)2. Thus, the above equation becomes:

y - c = a ( (x + b/2a)2 - b2/4a2)

Distributing "a" on the right side and adding "c" on both sides:

y = a (x + b/2a)2 - b2/4a + c

y = a (x + b/2a)2 - (b2 - 4ac) / (4a)

Comparing this with y = a (x - h)2 + k, we get:

h = -b/2a

k = -(b2 - 4ac) / (4a)

We know that b2 - 4ac is the discriminant (D).

Thus, the vertex formula is: (h, k) = (-b/2a, -D/4a) where D = b2 - 4ac

Formula 2

If you feel difficult to memorize the above formula, you can just remember the formula for the x-coordinate of vertex and then just substitute it in the given equation y = ax2 + bx + c to get the y-coordinate of the vertex.

x-coordinate of the vertex(h) = -b / 2a

Alternatively, if you do not want to use any of the above formulas to find the vertex, then you can just complete the square to convert y = ax2 + bx + c of the form y = a(x - h)2 + k manually and find the vertex (h, k).

Vertex Formula - What is Vertex Formula? Examples (1)

Vertex Formula - What is Vertex Formula? Examples (2)

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Examples Using Vertex Formula

  1. Example 1: Find the vertex of y = 3x2 - 6x + 1.

    Solution:

    To find: The vertex of the given equation (parabola).

    Comparing the given equation with y = ax2 + bx + c, we get

    a = 3, b = -6, c = 1.

    Then the discriminant is, D = b2 - 4ac = (-6)2 - 4(3)(1) = 36 - 12 = 24.

    Using the vertex formula (formula 1),

    Vertex, (h, k) = (-b/2a, -D/4a)

    (h, k) =( -(-6) / (2×3), -24 / (4×3) ) = (6/6, -24/12) = (1, -2)

    Therefore, The vertex of the given parabola = (1, -2).

  2. Example 2: Find the vertex of a parabola whose x-intercepts are (2, 0) and (3, 0) and whose y-intercept is (0, 6).

    Solution:

    To find: The vertex of the parabola.

    Since (2, 0) and (3, 0) are the x-intercepts of the given parabola, (x - 2) and (x - 3) are the factors of the equation of the parabola. So the equation of the parabola is of the form:

    y = a (x - 2) (x - 3) .... (1)

    Its y-intercept is given to be (0, 6). Substitute x = 0 and y = 6 in the above equation:

    6 = a (0 - 2) (0 - 3)

    6 = 6a

    a = 1

    Substitute a = 1 in (1):

    y = 1 (x - 2) (x - 3) = x2 - 5x + 6 ... (2)

    Comparing the above equation with y = ax2 + bx + c, we get

    a = 1; b = -5; c = 6

    Using the vertex formula (formula 2),

    x-coordinate of the vertex = -b / 2a = -(-5) / (2×1) = 5/2

    Substitute this in (2) to find the y-coordinate of the vertex.

    y = (5/2)2 - 5 (5/2) + 6 = -1/4

    Therefore, The vertex of the given parabola = (5/2, -1/4)

  3. Example 3: Determine the coordinates of the vertex for the given parabola equation: y= 4x2 + 16x -16

    Solution:

    Given equation: y= 4x2 + 16x -16

    Here a = 4, b = 16

    We know that the formula to find the x- coordinate is given by -b/2a

    = -16/2(4)

    = -2

    Therefore, x -coordinate is -2

    Now, substitute the value of x in the given equation, we get

    y = 4(-2)2 +16(-2) -16

    y= -32

    Hence, the vertex coordinates (h, k) is (-2, -32)

Show Solution >

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FAQs on Vertex Formula

What is Vertex Formula?

The Vertex formula of a parabola is used to find the coordinates of the point where the parabola crosses its axis of symmetry. The coordinates are given as (h,k). The vertex of a parabola is a point at which the parabola is minimum (when the parabola opens up) or maximum (when the parabola opens down) and the parabola turns (or) changes its direction.

What is the Formula to Find the Vertex on X Coordinates?

Using the standard form of a parabola y = ax2 + bx + c and the vertex equation y = a(x - h)2 + k, we can derive at the first formula of vertex i.e.

The vertex formula is: (h, k) = (-b/2a, -D/4a) where D= b2 - 4ac

How do you Use Vertex Formula?

Vertex formula can be used to find the vertex of any parabola using the parabola equation. The vertex formula for parabola equationy = ax2 + bx + c is given as, (h, k) = (-b/2a, -D/4a) where D= b2 - 4ac

What is the Formula to Find the Vertex on Y Coordinates?

To find the vertex (h, k), get h(x-coordinate of the vertex) = -b/2a from the standard equation y = ax2 + bx + c and then find y at h to get k (the y-coordinate of the vertex).

What is the Alternative Formula used to Find the Vertex?

The vertex formula to find the vertex coordinates (h,k)= (-b/2a, -D/4a) from the standard equation y = ax2 + bx + c, where D = b2 - 4ac.

Vertex Formula - What is Vertex Formula? Examples (2024)

FAQs

Vertex Formula - What is Vertex Formula? Examples? ›

The vertex formula helps to find the vertex coordinates of a parabola. The standard form of a parabola is y = ax2 + bx + c. 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).

What is the vertex formula 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.

What is an example of a vertex? ›

Vertices in shapes are the points where two or more line segments or edges meet (like a corner). The singular of vertices is vertex. For example, a cube has 8 vertices and a cone has one vertex. Vertices are sometimes called corners but when dealing with 2d and 3d shapes, the word vertices is preferred.

How to find the vertex in vertex form? ›

To find the vertex of a parabola that is in vertex form y = a (x - h)2 + k:
  1. Compare the given equation with y = a (x - h)2 + k and identify the values of h and k.
  2. (h, k) is the vertex.

What is the vertex symmetry formula? ›

What is the Axis of Symmetry Formula for Vertex Form? The quadratic equation is represented in the vertex form as: y = a(x−h)2 + k , where (h, k) is the vertex of the parabola. Since the axis of symmetry and the vertex form lie on the same line, the formula is x = h.

What is a common vertex example? ›

Two examples showing what the common vertex is

In the figure below, we see 2 angles named a and b. The common vertex for these two angles is the red dot that you see. In the figure below, we see 4 angles named 1, 2, 3, 4. The common vertex for these four angles is the red dot that you see.

What is a vertex set example? ›

A graph consists of two finite sets, V and E. Each element of V is called a vertex (plural vertices). The elements of E, called edges, are unordered pairs of vertices. For instance, the set V might be {a, b, c, d, e, f, g, h}, and E might be {{a, d}, {a, e}, {b, c}, {b, e}, {b, g}, {c, f}, {d, f}, {d, g}, {g, h}}.

How is the vertex calculated? ›

Get the equation in the form y = ax2 + bx + c. Calculate -b / 2a. This is the x-coordinate of the vertex. 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 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 convert 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 to vertex rule? ›

Vertex-to-vertex rule.

Each triangle must share two vertices with each of its adjacent triangles. In other words, a vertex of one triangle cannot lie on the side of another.

What is the vertex of this figure? ›

The vertex of a 2D figure is the point of intersection of two sides of the shape. The two sides of the shape or figure meet to form an angle, and thus a vertex is formed.

What is the formula for a parabola? ›

The standard equation of a parabola is used to represent a parabola algebraically in the coordinate plane. The general equation of a parabola can be given as, y = a(x-h)2 + k or x = a(y-k)2 +h, where (h,k) denotes the vertex. The standard form of parabola is y2 = 4ax or x2 = 4ay.

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