Factorising Quadratics
Quadratic expressions, which are an integral part of algebra, illustrate the nuance and complexity of mathematical formulas.
The process of factorizing quadratics is not only a mathematical operation, but it is a problem-solving tool that finds a variety of applications in scientific, engineering, as well as economic problems.
In this article, we will discuss:
Here is one more link to practice a few extra questions: Maths Genie Factorising Quadratics Questions
“a” is the coefficient of the x2 term,
“b” is the coefficient of the x-term;
“c” represents the constant term.
The highest power of a quadratic expression is 2.
If there are powers of x raised higher (like x3 or more), it is not a quadratic expression.
Monic Quadratic Expression (a = 1):
When the coefficient of x2 is 1 (for example x2 – 4x – 12), it will be known as a “monic” quadratic expression.
Non-Monic Quadratic Expression (a ≠ 1):
If the x2 coefficient is not 1 (for example, 3x2 – 4x – 12), it is referred to as a “non-monic” quadratic expression.
The expression with the form (x2 + bx + c) can be done by two brackets as (x + d)(x + e).
Expression vs. Equation:
A quadratic expression (math phrase including variables, constants, and operations) is a mathematical expression.
A quadratic equation in general may be interpreted as the declaration of equality of two expressions with ‘ax2 + bx + c = 0′ in particular.
Sometimes factoring of the numbers is used in solving quadratic equations by finding the values of x that make the equation correct.
Using the double brackets, we can factorize the quadratic expression as x2 + bx + c.
The process where factorization is found is the opposite of the operation in which double brackets are expanded. The case when the coefficient right after the x2 term is a = 1, is termed monic quadratic.
Method #1: Factorising “by inspection”
To factorize a quadratic expression, like x2 + 6x + 9, follow these steps:
Identify coefficients:
The quadratic expression is x2 + bx + c.
In this example, b is 6, and c is 9.
Find two numbers:
Find the pair of numbers that multiply to c (9) and add up to b (6).
3 x 3 = 9
and
3 + 3 = 6
Write in brackets:
Place these numbers in the brackets like this.
In fact, through observation, you can see that this expression can be factorized either as (x + 3)(x + 3) or as (x + 3)2.
Method 2: Factorising “by grouping”
Identify coefficients:
The coefficient, b is -4, and the y-intercept, c is -12.
Find two numbers:
Consider a set of numbers that when multiplied together result in c (-12), and when added together will equal b (-4).
The values of -6 and +2 satisfy these conditions.
(-6) x 2 = -12
and
(-6) + 2 = -4
Rewrite the middle term:
Rewrite the middle term of the quadratic expression in terms of the two numbers you have identified while factoring.
x2 – 6x + 2x – 12
Group and factorize:
Split terms into groups by two and then out of the pairs find the common factor.
(x(x – 6) + 2(x – 6))
Factor out common factors:
One can notice that both the terms have a common factor of (x – 6) now.
Factor out (x – 6):
(x – 6)(x + 2).
Hence, you can factor this x2 – 4x – 12 as (x – 6)(x + 2).
Solved Example:
Question 1: Factorize x2 – 13x + 36.
Solution:
The quadratic expression is x2 -13x + 36.
The coefficient, b is -13 and c = 36.
Seek a pair of numbers that, when multiplied, equal to c (36) and when added, equal to b (-13).
The numbers are -9 and -4 since
(-9) x (-4) = 36
and
(-9) + (-4) = -13
Express the midterm of the quadratic expression with the two factors determined through the process of factorization
x2 – 9x – 4x + 36
Group the terms in pairs and extract the common factor from each pair.
Factor out x from the first two terms and -4 from the last two terms:
(x(x – 9) -4(x – 9))
See that we have a common term for both expressions, that is, (x – 9).
Factor out (x – 9):
(x – 9)(x – 4).
So, by grouping, you can factorize x2 – 13x + 36 as (x – 9)(x – 4).
Question 1. Factorize x2 + 7x + 12
Answer : ( )( )The quadratic expression is x2 + 7x + 12
The coefficient, b is 7, and c is 12.
Look for a pair of numbers that multiply to c (12) and add up to (7).
The numbers are 3 and 4 because
3 x 4 = 12 and 3 + 4 = 7
Rewrite the middle term of the quadratic expression using the two numbers found.
x2 + 3x + 4x + 12
Group the terms into pairs and factor out the common factor from each pair.
Factor out x from the first two terms and 4 from the last two terms:
(x(x + 3) +4(x + 3))
Notice that both terms now have a common factor of (x + 3).
Factor out (x + 3):
(x + 3)(x + 4).
So, by grouping, you can factorize x2 + 7x + 12 as (x + 3)(x + 4).
Question 2: Factorize x2 + 8x + 15
Answer : ( )( )Solution:
The quadratic expression is x2 + 8x + 15
The coefficient, b is 8, and c is 15.
Look for a pair of numbers that multiply to c (15) and add up to (8).
The numbers are 3 and 5 because
3 x 5 = 15 and 3 + 5 = 8
Rewrite the middle term of the quadratic expression using the two numbers found.
x2 + 3x + 5x + 15
Group the terms into pairs and factor out the common factor from each pair.
Factor out x from the first two terms and 5 from the last two terms:
(x(x + 3) +5(x + 3))
Notice that both terms now have a common factor of (x + 3).
Factor out (x + 3):
(x + 3)(x + 5).
So, by grouping, you can factorize x2 + 8x + 15 as (x + 3)(x + 5).
To factorize quadratic expressions in the form ax2 + bx + c, apply the double brackets twice. Factorization is the opposite of expanding double brackets.
When the coefficient in front of the x2 term (a greater than 1) is greater than 1, it’s a non-monic quadratic formula.
Solved Example:
Question: Factorize 5x2 – 13x – 6
Solution:
Multiply the coefficients of the x2 term (5) and the constant term (-6):
5 x (-6) = -30
Write out the factor pairs of -30 in order:
(-1,30), (-2, 15), (-3, 10), (-5, 6).
Look for a pair of factors from step 1 that add up to the coefficient of the x term (-13).
The pair is (-15,2) because (-15) + 2 = -13
Rewrite the original expression, splitting the middle term into the two factors found in step #2
5x2 – 15x + 2x – 6
Split the equation down the middle:
5x2 – 15x and 2x – 6.
Fully factorize each half:
5x(x – 3) and 2(x – 3).
Factorize the whole expression by bringing the contents of the brackets to the front and writing the two other terms in the other bracket.
(5x + 2)(x – 3)
So, the solution to 5x2 -13x -6 by factorizing into double brackets is (5x + 2) (x – 3)
Question 1. Factorize 2x2 + 9x + 10
Answer : ( )( )The quadratic expression is 2x2 + 9x + 10.
The coefficient of x2 (a) is 2, the coefficient of x (b) is 9, and the constant term (c) is 10.
Multiply the coefficient of x2 by the constant term:
2 x 10 = 20
Identify factor pairs of 20 that add up to the coefficient of x(9).
The pair is (5, 4) because 5 x 4 = 20 and 5 + 4 = 9
Rewrite the middle term using the factor pairs:
2x2 + 5x + 4x + 10
Group the terms in pairs and extract the common factor from each pair:
x(2x + 5) + 2(2x + 5).
Factor out the common factor (2x + 5)
(2x + 5) (x + 2)
So, the quadratic expression 2x2 + 9x + 10 factors into (2x + 5)(x + 2).
Question 2: Factorize 5x2 + 26x + 5
Answer : ( )( )Solution:
The quadratic expression is 5x2 + 26x + 5.
The coefficient of x2 (a) is 5, the coefficient of x (b) is 26, and the constant term (c) is 5.
Multiply the coefficient of x2 by the constant term:
5 x 5 = 25
Identify factor pairs of 25 that add up to the coefficient of x(26).
The pair is (1, 25) because 1 x 25 = 25 and 1 + 25 = 26
Rewrite the middle term using the factor pairs:
5x2 + x + 25x + 5
Group the terms in pairs and extract the common factor from each pair:
x(5x + 1) + 5(5x + 1).
Factor out the common factor (5x + 1)
(5x + 1) (x + 5)
So, the solution of 5x2 + 26x + 5 by factorizing is (5x + 1)(x + 5)
Factorising quadratics is one of the important skills for a deeper understanding of algebraic statements.
Comprehension of factorisation entails a unique mathematical instrument that can be used in numerous disciplines.
This skill is varied from basic to creative mathematics.
Question 1: Factorize x2 + 10x + 25
Question 2: Factorize x2 + 9x + 14
Question 3: Factorize 2x2 + 17x + 36
Question 4: Factorize 5x2 + 62x + 24
Question 5: Factorize 7x2 + 10x + 3