Algebra Formulas For Class 8

Algebra Formulas For Class 8

Edited By Team Careers360 | Updated on Jul 02, 2025 05:16 PM IST

Algebraic Formulas are algebraic equations which are true for each and every value of the variable in it. The algebraic formulas that are valid for all values of variables in it are called algebraic identities. These identities are used to factorize polynomials and are used to compute algebraic expressions and solve different polynomials.

Algebraic expressions are known as collections of constants and variables connected to one or more operations like addition, subtraction, multiplication, and division. This expression contains monomial, binomial, trinomial and multinomial.Here monomial means having one term, binomial means having two terms, trinomial means having three terms, and multinomial means having more than three terms.

  • Constants which means a symbol having a fixed value.

  • Variables are collections of symbols that can give various numerical values.

  • Factor means quantities multiplied by each other to give a product and that product is known as a factor.

  • A factor of a non-constant term of an algebraic expression is called the coefficient of the remaining factor of a term. And these coefficients are of two types one is a numerical coefficient and another one is a literal coefficient.

Polynomials are of three types:

  • Linear polynomials having degree one.

  • Quadratic polynomial having degree two.

  • Cubic polynomial having degree three.

Algebraic Formulas

  1. (a + b)^{2} = a^{2} + 2ab + b^{2}

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  1. (a - b)^{2} = a^{2} - 2ab + b^{2}

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  1. (a+b)(a - b) = a^{2} - b^{2}

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  1. (x+a)(x+b) = x^{2} + (a+b)x + ab

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  1. (x+a)(x-b) = x^{2} + (a-b)x - ab

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  1. (x-a)(x+b) = x^{2} + (b-a)x - ab

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  1. (x-a)(x-b) = x^{2} - (a+b)x + ab

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  1. (a+b)^{3} = a^{3} + b^{3} + 3ab(a+b)

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  1. (a-b)^{3} = a^{3} - b^{3} - 3ab(a-b)

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  1. (a+b+c)^{2} = a^{2} + b^{2} + c^{2} + 2ab + 2bc + 2ac

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  1. (a+b-c)^{2} = a^{2} + b^{2} + c^{2} + 2ab - 2bc - 2ac

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  1. (a-b+c)^{2} = a^{2} + b^{2} + c^{2} - 2ab - 2bc + 2ac

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  1. (a-b-c)^{2} = a^{2} + b^{2} + c^{2} - 2ab + 2bc - 2ac

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Examples

(x+2)(x+5)

To solve this we can use a formula called: (x+a)(x+b) = x^{2} + (a+b)x + ab

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Here a = 2 and b = 5


(x+2)(x+5) = x^{2} + (2+5)x + 10

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(x+2)(x+5) = x^{2} + (7)x + 10

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Hence, (x+2)(x+5) equals to x^{2} + (7)x + 10.

  1. (x-3)(x+7)

To solve this we can use a formula called: (x-a)(x+b) = x^{2} + (b-a)x - ab

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Here a = 3 and b = 7


(x-3)(x+7) = x^{2} + (7-3)x - 21

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(x-3)(x+7) = x^{2} + 4x - 21


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Hence, (x-3)(x+7) equals to x^{2} + 4x - 21.

Frequently Asked Questions (FAQs)

1. What are Algebraic Formulas?

Algebraic Formulas are the generalized arithmetic equations formed by mathematical symbols and phrases.

2. What is an Exponent?

An Exponent defines how many times a number gets multiplied by itself. For Example, 2^{3} which specifies 2*2*2 = 8.

3. What is the difference between constants and variables?

The difference between a constant and a variable is that a constant has a fixed value while a variable has a value that can be varied.

4. What is the degree of a cubic polynomial?

The degree of a cubic polynomial is 3.

5. What are the five basic laws of Algebra?

They are: 

  • Associative Rule of Multiplication

  • Associative Rule of Addition.

  • Commutative Rule of Multiplication.

  • Commutative Rule of Addition.

  • Distributive Rule of Multiplication.

6. What is the FOIL method, and when is it used?
FOIL (First, Outer, Inner, Last) is a mnemonic device for multiplying two binomials. It reminds you to multiply each term of one binomial by each term of the other. For example, (x + 2)(x - 3) = x² - 3x + 2x - 6 = x² - x - 6. It's used specifically for binomial multiplication but is just a special case of the distributive property.
7. What is a polynomial and how is it different from other algebraic expressions?
A polynomial is an algebraic expression consisting of variables and coefficients, using only addition, subtraction, and multiplication operations. Unlike other algebraic expressions, polynomials do not involve division by variables or negative exponents. For example, 3x² + 2x - 5 is a polynomial, while 2x / (x+1) is not.
8. How can you determine the degree of a polynomial with multiple variables?
The degree of a polynomial with multiple variables is the highest sum of exponents in any term. For example, in the polynomial 2x²y³ + 3xy² - 5, the degree is 5 because the term x²y³ has the highest sum of exponents (2 + 3 = 5).
9. Can a constant be considered a polynomial? Why or why not?
Yes, a constant can be considered a polynomial. It's a special case where the degree is 0. For example, 5 can be thought of as 5x⁰, which is a polynomial of degree 0. This concept is important when working with polynomial operations and equations.
10. How do you add or subtract polynomials, and why does it work?
To add or subtract polynomials, you combine like terms (terms with the same variables and exponents). This works because of the distributive property and the fact that you can only add or subtract similar quantities. For example, (3x² + 2x - 1) + (x² - 3x + 4) = 4x² - x + 3.
11. Why are the terms in a polynomial arranged in descending order of degree?
Arranging terms in descending order of degree (highest to lowest) is a standard convention that makes polynomials easier to read, compare, and work with. It helps in quickly identifying the degree of the polynomial and its leading term. For instance, writing 2x³ - 4x + 1 + 5x² is clearer when arranged as 2x³ + 5x² - 4x + 1.
12. What's the difference between a monomial, binomial, and trinomial?
These terms refer to the number of terms in a polynomial:
13. What's the difference between a polynomial expression and a polynomial equation?
A polynomial expression is a mathematical phrase involving variables and coefficients, like 2x² + 3x - 5. A polynomial equation sets a polynomial expression equal to another expression (often zero), like 2x² + 3x - 5 = 0. Equations are statements that can be solved, while expressions are simply mathematical phrases.
14. Why is the zero polynomial considered to have no degree?
The zero polynomial (0) is a special case. It has no degree because it has no non-zero terms. Mathematically, we say its degree is undefined or -∞. This distinction is important in various polynomial theorems and operations.
15. How does the degree of a polynomial affect its graph?
The degree of a polynomial determines the basic shape of its graph and how many times it can cross the x-axis:
16. Why can't we divide by zero in polynomial expressions?
Division by zero is undefined in mathematics because it leads to logical contradictions. In polynomial expressions, dividing by zero (or by a factor that could be zero) can result in undefined behavior or loss of information about the polynomial's behavior at certain points.
17. What's the significance of the leading coefficient in a polynomial?
The leading coefficient is the coefficient of the highest-degree term. It's significant because:
18. What's the difference between real and complex roots of a polynomial?
Real roots are solutions to a polynomial equation that are real numbers. Complex roots come in conjugate pairs and involve imaginary numbers. For example, x² + 1 = 0 has no real roots, but it has two complex roots: i and -i. Understanding this difference is crucial for fully describing a polynomial's behavior.
19. What's the relationship between the degree of a polynomial and its x-intercepts?
The degree of a polynomial is the maximum number of real x-intercepts (roots) it can have. However, it may have fewer due to:
20. Why is the concept of multiplicity important in understanding polynomial roots?
Multiplicity refers to how many times a particular root occurs in a polynomial. It's important because:
21. What's the connection between polynomial long division and synthetic division?
Polynomial long division and synthetic division are both methods for dividing polynomials, but:
22. How do you determine if a polynomial is factorable over the real numbers?
To determine if a polynomial is factorable over the real numbers:
23. How does the concept of polynomial interpolation relate to finding a polynomial function?
Polynomial interpolation is the process of finding a polynomial that passes through a given set of points. It relates to finding a polynomial function because:
24. What's the significance of the Fundamental Theorem of Algebra for polynomials?
The Fundamental Theorem of Algebra states that every non-constant polynomial with complex coefficients has at least one complex root. Its significance includes:
25. How do you interpret the coefficients of a polynomial in context?
Interpreting coefficients depends on the context:
26. Why can't all polynomials be factored using real numbers?
Not all polynomials can be factored using real numbers because:
27. How does the concept of a polynomial's zeros relate to its factors?
A polynomial's zeros (roots) are directly related to its factors:
28. What's the relationship between a polynomial's degree and its end behavior?
A polynomial's end behavior (its graph's tendency as x approaches ±∞) is determined by its degree and leading coefficient:
29. How do you determine the multiplicity of a root without fully factoring the polynomial?
To determine a root's multiplicity without full factoring:
30. How does the concept of a polynomial's turning points relate to its derivative?
A polynomial's turning points (local maxima and minima) are closely related to its derivative:
31. What's the significance of the Rational Zero Theorem in polynomial algebra?
The Rational Zero Theorem is significant because:
32. Why can't you cancel terms when adding fractions with polynomial numerators?
You can't cancel terms when adding fractions with polynomial numerators because the terms are being added, not multiplied. Cancellation only applies to factors, not terms. For example, in (x² + 3) / 5 + (2x - 1) / 5, you can't cancel the x² with the 2x; instead, you add the numerators: (x² + 3 + 2x - 1) / 5.
33. How does factoring relate to the roots of a polynomial equation?
Factoring a polynomial reveals its roots. When you factor a polynomial and set each factor to zero, you find the values of x that make the polynomial equal to zero. These values are the roots of the polynomial equation. For example, if x² - 4 = 0 factors to (x+2)(x-2) = 0, the roots are x = 2 and x = -2.
34. What's the relationship between the coefficients and roots of a polynomial?
The coefficients of a polynomial are related to its roots through Vieta's formulas. For a quadratic ax² + bx + c = 0 with roots r and s:
35. How do you determine if a polynomial is even or odd?
A polynomial P(x) is even if P(-x) = P(x) for all x, and odd if P(-x) = -P(x) for all x. In practice:
36. How does factoring help in solving polynomial equations?
Factoring helps solve polynomial equations by breaking them down into simpler parts. When you factor a polynomial and set it to zero, you can use the zero product property: if a product is zero, at least one of its factors must be zero. This allows you to solve complex equations by solving simpler linear equations.
37. How do you determine the number of real roots a polynomial has without solving it?
The number of real roots can be determined using:
38. Why is the Remainder Theorem useful in polynomial division?
The Remainder Theorem states that the remainder of a polynomial P(x) divided by (x - a) is equal to P(a). This is useful because:
39. How does the concept of a polynomial function differ from a polynomial expression?
A polynomial expression is a mathematical phrase involving variables and coefficients. A polynomial function assigns a unique output value to each input value using a polynomial expression. For example, f(x) = x² + 2x - 3 is a polynomial function that takes an input x and produces an output based on the expression x² + 2x - 3.
40. How do you interpret the graph of a polynomial in terms of its algebraic properties?
The graph of a polynomial reveals several algebraic properties:
41. How does the Rational Root Theorem help in finding polynomial roots?
The Rational Root Theorem states that if a polynomial equation with integer coefficients has a rational solution, it will be of the form ±p/q, where p is a factor of the constant term and q is a factor of the leading coefficient. This narrows down the possible rational roots, making it easier to find them through testing or other methods.
42. Why is the concept of a polynomial identity important?
A polynomial identity is an equation that is true for all values of its variables. It's important because:
43. Why is the discriminant useful in analyzing quadratic polynomials?
The discriminant (b² - 4ac for ax² + bx + c) is useful because:

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