# Midpoint Formula

• Introduction to Midpoint Formula
• What is the Midpoint?
• Exploring the Midpoint Formula
• Ways to Find the Midpoint of a Line Segment
• Understanding the Centroid of a Triangle
• Understanding the Section Formula
• Important Points
• Solved Questions
• Practice Problems

## Introduction to Midpoint Formula

The midpoint formula is a fundamental concept in geometry used to determine the middle point between two given points on a coordinate plane. It is a crucial tool in various mathematical applications, such as calculating distances, determining center points, and solving geometric problems. By understanding and utilizing the midpoint formula, mathematicians and students can efficiently analyze geometric figures and solve problems related to spatial relationships.

## What is the Midpoint Formula?

A midpoint formula represents the point positioned between two other points, precisely at the center of the line connecting them. It is equidistant from both ends of the line segment. Imagine drawing a line between two points; the midpoint lies directly in the middle of that line. For any given pair of points, like A and C, the midpoint, denoted as B, is situated halfway between them. This means the distance from A to B is equal to the distance from B to C. To find the length of AB or BC, we can measure the entire length of the line segment and divide it by 2.

## Exploring the Midpoint Formula

The midpoint formula is a mathematical tool used to determine the coordinates of the midpoint between two given points on a coordinate plane. This formula is particularly useful in geometry and various real-world applications involving spatial relationships. We can precisely locate the center point between two given points by applying the midpoint formula.

The formula for finding the midpoint between two points $$(x_1, y_1)$$ and $$(x_2, y_2)$$ is:

$$\text{Midpoint} = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right)$$

In this formula, $$x_1$$ and $$x_2$$ represent the x-coordinates of the given points, while $$y_1$$ and $$y_2$$ represent their y-coordinates. By substituting the coordinates of the given points into this formula, we can easily calculate the coordinates of the midpoint.

Example: We have two points on a coordinate plane, $$P(2, 4)$$ and $$Q(6, 8)$$. Find the coordinates of the midpoint M between these two points.

Solution:

To find the midpoint between two points $$(x_1, y_1)$$ and $$(x_2, y_2)$$, we can use the midpoint formula:

$$\text{Midpoint} = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right)$$

Given $$P(2, 4)$$ and $$Q(6, 8)$$, we substitute the coordinates into the formula:

$$\text{Midpoint} = \left( \frac{2 + 6}{2}, \frac{4 + 8}{2} \right)$$

$$\text{Midpoint} = \left( \frac{8}{2}, \frac{12}{2} \right)$$

$$\text{Midpoint} = (4, 6)$$

Therefore, the coordinates of the midpoint between points $$P$$ and $$Q$$ are $$M(4, 6)$$.

## Ways to Find the Midpoint of a Line Segment

Method 1: Simple Distance Division

If the line segment is vertical or horizontal, a straightforward approach is to divide its length by 2 and count that distance from either endpoint. For instance, consider points A(-3, 2) and B(1, 2) on a horizontal line. Since the line is horizontal, we can simply divide the length (which is 4 units in this case) by 2 to get 2 units. Starting from point A(-3, 2), moving 2 units horizontally lands us at the midpoint (-1, 2).

Method 2: Using the Midpoint Formula

Another method involves utilizing the midpoint formula, particularly useful for any orientation of the line segment. Given points A(-3, -3) and B(1, 4), we apply the midpoint formula:

$$\text{Midpoint} = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right)$$

Substituting the coordinates into the formula, we find the midpoint to be (-1, 1/2).

Method 3: Construction Technique

Alternatively, a geometric construction method involves using a compass and straightedge. First, create circular arcs with the same radius centered at each endpoint. Then, connect the points where the arcs intersect to form a lens shape. Finally, draw a straight line connecting the cusps of the lens. The point where this line intersects the line segment is the midpoint.

## Understanding the Centroid of a Triangle

The centroid of a triangle is a point where the three medians intersect. A median of a triangle is a line segment joining a vertex to the midpoint of the opposite side. The centroid is often referred to as the "center of mass" or the "center of gravity" of the triangle. It divides each median into two segments, with the segment adjacent to the vertex being twice as long as the segment adjacent to the midpoint of the opposite side.

Formula for Finding the Centroid

Given a triangle with vertices $$A(x_1, y_1)$$, $$B(x_2, y_2)$$, and $$C(x_3, y_3)$$, the coordinates of the centroid $$G$$ can be found using the following formula:

$$G \left( \frac{x_1 + x_2 + x_3}{3}, \frac{y_1 + y_2 + y_3}{3} \right)$$

This formula calculates the average of the x-coordinates and y-coordinates of the three vertices, providing the coordinates of the centroid $$G$$ as the midpoint of the triangle's medians.

Example: Let's consider a triangle with vertices $$A(2, 4)$$, $$B(6, 8)$$, and $$C(10, 2)$$. Find the coordinates of the centroid $$G$$ of this triangle.

Solution:

To find the centroid $$G$$ of the triangle, we'll use the centroid formula, which averages the coordinates of the three vertices:

$$G \left( \frac{x_1 + x_2 + x_3}{3}, \frac{y_1 + y_2 + y_3}{3} \right)$$

Given the coordinates of $$A(2, 4)$$, $$B(6, 8)$$, and $$C(10, 2)$$, we substitute these values into the formula:

$$G \left( \frac{2 + 6 + 10}{3}, \frac{4 + 8 + 2}{3} \right)$$

$$G \left( \frac{18}{3}, \frac{14}{3} \right)$$

$$G \left( 6, \frac{14}{3} \right)$$

Therefore, the coordinates of the centroid $$G$$ of the triangle with vertices $$A(2, 4)$$, $$B(6, 8)$$, and $$C(10, 2)$$ are $$G(6, \frac{14}{3})$$.

## Understanding the Section Formula

The Section Formula is a mathematical principle used to find the coordinates of a point that divides a line segment into two parts, given the coordinates of the endpoints of the segment and the ratio in which it is divided.

The formula for finding a point using the section formula

Let's say we have a line segment with endpoints $$A(x_1, y_1)$$ and $$B(x_2, y_2)$$, and a point $$P$$ divides the line segment in the ratio $$m:n$$. The coordinates of point $$P$$ can be calculated using the section formula:

$$P \left( \frac{mx_2 + nx_1}{m+n}, \frac{my_2 + ny_1}{m+n} \right)$$

In this formula:

• $$m$$ and $$n$$ represent the ratios in which the line segment $$AB$$ is divided.
• $$m$$ and $$n$$ are typically positive integers, but they can be any real numbers as long as $$m + n \neq 0$$.
• The sum $$m + n$$ represents the total number of parts into which the line segment is divided.
• The coordinates of point $$P$$ are the weighted averages of the coordinates of $$A$$ and $$B$$, where the weights are determined by the ratios $$m$$ and $$n$$.

Example: We have a line segment with endpoints $$A(3, 2)$$ and $$B(9, 6)$$. Find the coordinates of a point $$P$$ that divides the segment in the ratio $$2:3$$.

Solution:

To find the coordinates of point $$P$$, we'll use the section formula, which calculates the coordinates of a point dividing a line segment according to a given ratio.

Given the coordinates of $$A(3, 2)$$ and $$B(9, 6)$$, and the ratio $$2:3$$, we can apply the formula:

$$P \left( \frac{mx_2 + nx_1}{m+n}, \frac{my_2 + ny_1}{m+n} \right)$$

where $$m = 2$$ and $$n = 3$$.

Substituting the given values into the formula, we get:

$$P \left( \frac{2 \cdot 9 + 3 \cdot 3}{2+3}, \frac{2 \cdot 6 + 3 \cdot 2}{2+3} \right)$$

$$P \left( \frac{18 + 9}{5}, \frac{12 + 6}{5} \right)$$

$$P \left( \frac{27}{5}, \frac{18}{5} \right)$$

Therefore, the coordinates of the point $$P$$ that divides the line segment joining $$A(3, 2)$$ and $$B(9, 6)$$ in the ratio $$2:3$$ are $$P\left(\frac{27}{5}, \frac{18}{5}\right)$$.

## Important Points

• Fundamental Principle: The midpoint formula determines the center point between two given points on a coordinate plane by averaging their x-coordinates and y-coordinates.
• Symmetrical Nature: It guarantees that the midpoint is equidistant from both endpoints, ensuring a balanced division of the line segment.
• Ease of Calculation: By simply adding and dividing the coordinates, it offers a straightforward method for finding the midpoint, aiding in various geometric computations.
• Geometric Interpretation: Understanding the midpoint aids in visualizing and analyzing spatial relationships in geometric shapes, facilitating problem-solving.
• Real-world Applications: Widely used in fields like engineering, architecture, and physics, its applications include determining center points, distances, and balancing structures.

## Solved Examples

Example 1. Find the midpoint of the line segment joining points A(4, 6) and B(10, 12).

Solution:

Using the midpoint formula:

$$\text{Midpoint} = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right)$$

Substituting the coordinates of A and B:

$$\text{Midpoint} = \left( \frac{4 + 10}{2}, \frac{6 + 12}{2} \right)$$

$$\text{Midpoint} = (7, 9)$$

Therefore, the midpoint of the line segment AB is (7, 9).

Example 2. Find the centroid of the triangle with vertices at (1, 1), (5, 3), and (7, 7).

Solution:

Using the centroid formula:

$$G \left( \frac{x_1 + x_2 + x_3}{3}, \frac{y_1 + y_2 + y_3}{3} \right)$$

Substituting the coordinates of the vertices:

$$G \left( \frac{1 + 5 + 7}{3}, \frac{1 + 3 + 7}{3} \right)$$

$$G \left( \frac{13}{3}, \frac{11}{3} \right)$$

Therefore, the centroid of the triangle is $$\left(\frac{13}{3}, \frac{11}{3}\right)$$.

Example 3. Determine the coordinates of the point that divides the line segment joining (-2, 4) and (6, -3) in the ratio 3:2.

Solution:

Using the section formula:

$$P \left( \frac{mx_2 + nx_1}{m+n}, \frac{my_2 + ny_1}{m+n} \right)$$

Substituting the given values:

$$P \left( \frac{3 \cdot 6 + 2 \cdot (-2)}{3+2}, \frac{3 \cdot (-3) + 2 \cdot 4}{3+2} \right)$$

$$P \left( \frac{18 - 4}{5}, \frac{-9 + 8}{5} \right)$$

$$P \left( \frac{14}{5}, \frac{-1}{5} \right)$$

Therefore, the point dividing the line segment in the ratio 3:2 is $$\left(\frac{14}{5}, \frac{-1}{5}\right)$$.

Example 4. Determine the endpoint B of a line segment with one endpoint at A (-3, 5) a midpoint at M (2, 2).

Solution:

We have one endpoint (point A) as (-3, 5) and the midpoint (M) as (2, 2).

The midpoint formula states that the midpoint of a line segment connecting points A (x_1, y_1) and B (x_2, y_2) is:

$$\text{Midpoint} (x, y) = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right)$$

Let point B be represented as (x_2, y_2). We can use the values of (-3, 5) for (x_1, y_1) and (2, 2) for (x, y) to find the coordinates (x_2, y_2):

$$\frac{-3 + x_2}{2} = 2$$

$$\frac{5 + y_2}{2} = 2$$

$$x_2 = 2 \times (2) - (-3) = 7$$

$$y_2 = 2 \times (2) - (5) = -1$$

Therefore, the endpoint B of the line segment is located at (7, -1).

Example 5. Find the point of bisection of the line segment AB, where A (-6, 11) and B (10, -3).

Solution:

The point of bisection of a line segment divides the line segment into 2 equal halves. Hence, we need to find the midpoint of line segment AB.

Using the midpoint formula:

$$\text{Midpoint} = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right)$$

Substituting the coordinates of A and B:

$$\text{Midpoint} = \left( \frac{-6 + 10}{2}, \frac{11 - 3}{2} \right)$$

$$\text{Midpoint} = (2, 4)$$

Therefore, the coordinates of the point of bisection of the line segment AB is (2, 4).

## Practice Problems

Q1. What is the midpoint of the line segment joining points A(4, 8) and B(10, 14)?

1. (7, 11)
2. (8, 12)
3. (9, 13)
4. (10, 14)

Q2. Determine the centroid of the triangle with vertices at (-2, 6), (3, 2), and (8, 10).

1. (4, 8)
2. (3, 6)
3. (2, 5)
4. (6, 6)

Q3. True or False: The point dividing the line segment joining (-3, 5) and (7, -1) in the ratio 2:3 is (1, 1).

1. True
2. False

Q4. Determine the coordinates of the point that divides the line segment joining (-5, 3) and (10, -2) in the ratio 4:1.

1. (23/5, -1/5)
2. (0, 1/5)
3. (12/5, 2)
4. (13/3, 25/3)

Q5. Find the centroid of the triangle with vertices at (0, 0), (6, 4), and (-3, 8).

1. (4, 8)
2. (3, 6)
3. (1, 4)
4. (4, 1)

Q1. What is the midpoint formula and how is it used?

Answer: The midpoint formula calculates the coordinates of the point that lies halfway between two given points on a line segment. It is used to find the center point or midpoint of a line segment, which is crucial in geometry and various applications such as computer graphics and engineering.

Q2. How do you find the centroid of a triangle?

Answer: The centroid of a triangle is the point where the three medians intersect. To find the centroid, you can use the centroid formula, which averages the x-coordinates and y-coordinates of the triangle's vertices. The coordinates of the centroid are the average of the coordinates of the three vertices.

Q3. What is the section formula and when is it used?

Answer: The section formula calculates the coordinates of a point that divides a line segment into two parts, given the coordinates of the endpoints and the ratio in which it is divided. It is used in geometry to find the coordinates of a point dividing a line segment according to a given ratio.

Q4. Can a line segment have negative coordinates in the midpoint formula?

Answer: Yes, a line segment can have negative coordinates in the midpoint formula. The midpoint formula calculates the average of the x-coordinates and y-coordinates of the endpoints, regardless of whether they are positive or negative. Negative coordinates simply indicate positions to the left or below the origin on a coordinate plane.

Q5. What are some real-world applications of the midpoint formula and centroid formula?

Answer: The midpoint formula and centroid formula have various real-world applications. For example, in architecture and construction, they are used to locate the center point of structures for balance and stability. In navigation and GPS systems, they help determine the midpoint of routes or distances between locations. Additionally, in computer graphics, they are used to position objects or elements within a frame for visual display.