Pascal's Triangle: Definition, Formula, Properties, Applications & Examples

Pascal’s Triangle is a special triangle made by arranging numbers in a pattern. It is named after the French mathematician Blaise Pascal. In this triangle, each number is the sum of the two numbers just above it from the previous row. The triangle starts with 1 at the top, and every row starts and ends with 1.

Pascal’s Triangle is very useful in math. It helps in solving problems in probability, algebra, and combinatorics (which is the study of counting). For example, it can be used to find the coefficients in binomial expansions (like when you expand (a+b)n. It’s also used to calculate the number of ways certain events can happen, like getting heads and tails when tossing coins.

Pascal Triangle

Pascal’s Triangle is a triangle-shaped pattern made up of numbers. Each row starts and ends with the number 1. The numbers in between are found by adding the two numbers directly above them from the row above. This pattern continues row by row.

Pascal’s Triangle is very useful in math, especially in probability, algebra, and combinatorics (which is the study of counting and arrangements). It helps us find the chances of certain outcomes—like in a coin toss—and is also used to get the coefficients when expanding expressions like (x+y)n.

For example, the third row of Pascal’s Triangle is 1, 2, 1, and these numbers are the coefficients in the expansion of (x + y)² = x² + 2xy + y².

Patterns of Pascal’s Triangle

Pascal’s triangle contains several patterns, some examples of Pascal triangle patterns are:

The following patterns are followed in Pascal’s triangle:

Each number is the sum of the numbers directly above it.

The first diagonal is made up of 1’s.

The second diagonal is made up of counting numbers, such as 1,2,3,4,…

The third diagonal contains triangular numbers such as 1, 3, 6, 10, 15, etc.

The fourth diagonal contains tetrahedral numbers such as 1,4,10,20, and so on.

Symmetrical

The triangle is symmetrical as well. Like a mirror image, the numbers on the left side have identical matching numbers on the right side.

Horizontal sums

Using the Pascal’s triangle formula to calculate the sum of the elements in the Pascal’s triangle’s row. They always double (powers of 2).

Square

The third diagonal contains square numbers. A square number is the sum of any two consecutive numbers in the triangle’s third row. When all of the circled numbers in the image are added up, they form a square number.

For example:

Fibonacci sequence

The Fibonacci numbers can be calculated by adding the elements of the Pascal’s triangle’s rising diagonal lines.

Pascal’s triangle formula

The Pascal’s triangle formula is:

Combinations are represented by this parenthetical notation, so another way to express would be

Construction of Pascal’s Triangle

To make the triangle, begin with a “1” at the top and continue with two 1’s on the next row, forming a triangle. Begin and end each subsequent row with a 1 and compute each interior term by adding the two numbers above it.

We will get a Pascal triangle if we repeat this process. This is an endless triangle.

Properties of Pascal’s Triangle

Pascal’s Triangle Properties are

• In Pascal’s Triangle, each number is the sum of the two numbers above it.
• The nature of numbers in a row is symmetric.
• The pascal’s triangle is also symmetric
• The sums of the rows give the powers of 2.
• A binomial coefficient is represented by each number.
• The numbers on the triangle’s left and right sides are always 1.
• The row contains numbers.

Pascal’s Triangle in Binomial Expansion

Pascal’s triangle can also be used to calculate the coefficients of terms in a binomial expansion. Pascal’s triangle is a useful tool for quickly determining whether or not the binomial expansion of a given polynomial is correct.

The coefficients in binomial expansions are defined by Pascal’s triangle. That is, the coefficients of the polynomial’s expanded expression are represented in the nth row of Pascal’s triangle

For example:

Expand this

Solution:

when comparing with the binomial formula then,

x = 2, b = 3x and n = 3

Expansion of is \left ( x+y \right )^{n} = a_{0}x^{n} + a_{1}x^{n-1}y + a_{2}x^{n-2}y^{2} + ..+ a_{n-1}xy^{n-1} + a_{n} y^{n} , where the coefficients of the form are the nth row of Pascal’s triangle. This can be stated as follows:

Application of Pascal’s Triangle

Pascal’s Triangle is a helpful tool in math and is used in many different ways. Here are some of its main uses:

• Binomial Expansion: When you expand something like (x + y) raised to a power, Pascal’s Triangle gives you the numbers (called coefficients) you need in the answer.
• Combinations: You can use Pascal’s Triangle to find how many ways things can be chosen or arranged, which is a big part of counting problems in math.
• Probability: It helps in figuring out chances in situations where there are only two outcomes, like flipping a coin and getting heads or tails.
• Number Patterns: Pascal’s Triangle shows interesting number patterns, like triangular numbers and even parts of the Fibonacci sequence.
• Computer Algorithms: Because of its repeating and structured pattern, it’s used in computer programs to quickly calculate things like combinations.

Pascal’s triangle is used extensively in mathematics and statistics. The binomial expansion can be found using Pascal’s triangle. Pascal’s triangle is also used in probabilistic applications and combination calculations.

We will look at the two coin toss examples here. In probability, Pascal’s triangle can be used to simplify counting the probabilities of an event. Pascal’s triangle, for example, can show us how many different ways we can combine heads and tails in a coin toss.

Example of Toss Two coins

Coin flip	Possible sequences of heads (H) or tails (T)	Pascal’s triangle
2	HH HT TH TT	1,2,1

There are 2\times 2= 4 possible heads/tails sequences after three coin flips.

When the sequences are sorted into groups of “how many heads (2, 1, or 0),” each group contains 1, 2, 1, and 1 sequences, respectively.

Example of Toss Three coins

Coin flip	Possible sequences of heads (H) or tails (T)	Pascal’s triangle
3	HHH HHT HTH THH HTT THT TTH TTT	1 3 3 1

There are 2\times 2\times 2 = 8 possible heads/tails sequences after three coin flips.

When the sequences are sorted into groups of “how many heads (3, 2, 1, or 0),” each group contains 1, 3, 3, and 1 sequences, respectively.

• Each number in Pascal's Triangle is found by adding the two numbers just above it in the row before.
• The total of all the numbers in the nth row is equal to 2ⁿ.
• Pascal's Triangle helps in finding the coefficients when expanding expressions like (a+b)n (called binomial expansions).

Pascals Triangle Solved Examples

Example 1: Find the sum of the numbers in the 5th row of Pascal’s Triangle.

Solution:
We use the formula:
Sum = 2ⁿ, where n is the row number.

Here, n = 5, so:
Sum = 2⁵ = 32

Answer: The sum of the numbers in the 5th row of Pascal’s Triangle is 32.

Example 2:With four coin tosses, what is the probability of obtaining exactly two heads?

Solution:

There are

1+4+6+4+1 = 16

There are 16 possible outcomes, and 6 of them produce exactly two heads.

As a result, the probability is

\( \frac{6}{16} = 37.5% \)

Example 3: A coin is tossed 4 times. What is the probability of getting exactly 3 heads?

Solution:
When a coin is tossed 4 times, the total number of possible outcomes is:
2⁴ = 16

Now, we look at how many of these outcomes give us exactly 3 heads.
From Pascal’s Triangle, the number of ways to get exactly 3 heads out of 4 tosses is 4.

So, the probability = 4/16 = 1/4 = 25%

Answer: The probability of getting exactly 3 heads is 25%.

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If you are checking Pascals triangle article, also check the related maths articles in the table below:
Concentric circles	Conjunction
Graphical representation	Sieve of eratosthenes
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