Every exponent must be a whole number.
In 3x² − 2x + 1 the exponents are 2, 1 and 0. The others have −1 or 1/2.
Class 9 · Maths · Chapter 2 · बिहार बोर्ड (BSEB)CBSE · NCERT 2026-27
Polynomials
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एक चर का बहुपद और घात — प्रश्नावली 2.1 · NCERT 2.2 · Exercise 2.1
A polynomial in one variable x is p(x) = aₙxⁿ + aₙ₋₁xⁿ⁻¹ + … + a₁x + a₀, with aₙ ≠ 0. Here n is a whole number. a₀, a₁, … are the coefficients. The terms run from aₙxⁿ down to a₀.
One term is a monomial, two terms a binomial, three terms a trinomial. Degree 1 is linear, of the form ax + b with a ≠ 0. Degree 2 is quadratic. Degree 3 is cubic. 5x² + 3x + π is quadratic, because π may be a coefficient.
x + 1/x = x + x⁻¹ is not a polynomial. Neither is √x + 4 = x1/2 + 4. A non-zero constant has degree 0. The degree of the zero polynomial is not defined.
| Name | Degree | Example |
|---|---|---|
| Constant | 0 | 7 |
| Linear | 1 | 4x + 7 |
| Quadratic | 2 | x² − 3x + 2 |
| Cubic | 3 | 2x³ − x |
Question: Find the degree of 2 − y² − y³ + 2y⁸. Also write the degree of the constant 5.
Step 1. Write the terms in descending degree: 2y⁸ − y³ − y² + 2.
Step 2. The highest power of the variable is 8. So the degree is 8.
Step 3. 5 is a non-zero constant. It has no variable, which means the coefficient of y⁰. The degree is 0.
Caution: If the polynomial is only 0, do not write a degree. It is not defined.
Before division, and when the degree is asked, arrange the terms in descending degree.
A coefficient may be irrational. πx² + 2 is a polynomial. The degree belongs to the variable, not to the coefficient.
Every exponent must be a whole number.
In 3x² − 2x + 1 the exponents are 2, 1 and 0. The others have −1 or 1/2.
False. A non-zero constant has degree 0. The degree of the zero polynomial is not defined.
A linear polynomial.
The highest power is 1.
Three terms, highest power 2.
There are three terms, so it is a trinomial. The degree is 2, so it is quadratic.
In 5x² + 3x + π the exponents are 2, 1 and 0, and π is a coefficient. It is a quadratic polynomial of degree 2. In √x + 1 the power of x is 1/2, which is not a whole number, so it is not a polynomial.
बहुपद का मान और शून्यक — प्रश्नावली 2.2 · NCERT 2.3 · Exercise 2.2
The number obtained by putting c in place of x in p(x) is p(c). If p(c) = 0, then c is a zero of the polynomial. The same c is a root of the equation p(x) = 0.
The linear polynomial ax + b has exactly one zero, x = −b/a. A non-zero constant has no zero, because 7 = 0 never holds. Every real number is a zero of the zero polynomial. That is the convention.
A polynomial can have more than one zero. The zeroes of x² − 2x are 0 and 2, because x(x − 2) = 0.
Question: Find one zero of p(x) = 2x + 1 and check it.
Step 1. For a zero put p(x) = 0: 2x + 1 = 0.
Step 2. 2x = −1, so x = −1/2.
Formula: The zero of ax + b is −b/a. Here a = 2 and b = 1, so −b/a = −1/2.
Check: p(−1/2) = 2×(−1/2) + 1 = −1 + 1 = 0. So −1/2 is a zero.
The zero of x + 2 is −2, not 2. The sign flips.
Value and zero are different. p(1) may be 4. A zero is only where the value is 0.
x − 3 = 0.
p(3) = 0. The zero is 3.
True. 4 is never 0. The zero polynomial is a different case.
Putting x = 0 leaves only the constant.
p(0) = 0 − 0 + 3 = 3.
p(−2) = −2 + 2 = 0, so −2 is a zero. p(2) = 2 + 2 = 4 ≠ 0, so 2 is not a zero.
भाग और शेषफल प्रमेय — प्रश्नावली 2.3 · NCERT 2.4 · Exercise 2.3
Polynomials are divided in the same spirit as numbers. In 15 = (6 × 2) + 3 the remainder is smaller than the divisor. For polynomials, p(x) = g(x) q(x) + r(x), and the degree of r is less than the degree of g.
If the divisor is a monomial, divide each term. Dividing 2x³ + x² + x by x gives 2x² + x + 1. But in 3x² + x + 1 the constant 1 does not divide by x into a polynomial term. The remainder stays 1 and x is not a factor.
Before dividing, write descending powers. Write x + 3x² − 1 as 3x² + x − 1. If the degree is at least 1 and the divisor is x − a, the remainder is p(a).
Question: Find the remainder when p(x) = x³ + 1 is divided by x + 1. Also show the long division.
Formula: x + 1 = x − (−1), so a = −1 and the remainder is p(−1).
Substitution: p(−1) = (−1)³ + 1 = −1 + 1 = 0.
Long division: The dividend is x³ + 0x² + 0x + 1. The first term is x². (x + 1)x² = x³ + x². Subtraction leaves −x². The next term is −x. (x + 1)(−x) = −x² − x. Subtraction leaves x. The next term is +1. (x + 1)(1) = x + 1. Subtraction leaves 0.
Answer: The quotient is x² − x + 1 and the remainder is 0. The two methods agree.
For x − 1 and x + 1 the value of a is different. Use p(1) for x − 1 and p(−1) for x + 1.
Write a missing power with coefficient 0, such as x² and x in x³ + 1.
Find p(2).
p(2) = 4 − 4 = 0.
False. x + 1 = x − (−1), so the remainder is p(−1).
p(1).
p(1) = 1 − 1 = 0.
Descending degree.
The standard form is 3x² + x − 1.
Cancel x in each term.
2x² + x + 1.
Formula: divisor x − a with a = 1, remainder p(1). p(1) = 1 + 1 − 2 + 1 + 1 = 2. The remainder is 2.
गुणनखंड प्रमेय और गुणनखंडन — प्रश्नावली 2.4 · NCERT 2.5 · Exercise 2.4
By the Remainder Theorem, p(x) = (x − a) q(x) + p(a). If p(a) = 0, then p(x) = (x − a) q(x). (x − a) is a factor if and only if p(a) = 0.
Split the middle term of ax² + bx + c into two numbers whose product is a×c and whose sum is b. Then take out the common bracket.
For a cubic, try factors of the constant. If p(1) = 0, then (x − 1) is a factor. Divide, leave a quadratic, and split that too.
Question: Factorise 6x² + 17x + 5 by splitting the middle term.
Step 1. a×c = 6×5 = 30 and b = 17. The two numbers are 15 and 2, because 15×2 = 30 and 15+2 = 17.
Step 2. 6x² + 15x + 2x + 5.
Step 3. 3x(2x + 5) + 1(2x + 5) = (3x + 1)(2x + 5).
Check: (3x + 1)(2x + 5) = 6x² + 15x + 2x + 5 = 6x² + 17x + 5.
If the question asks about the factor x + 2, put a = −2 and look at p(−2).
The signs of the split numbers follow the sum. If the sum is negative, both can be negative.
x + 2 = x − (−2).
p(−2) = −8 + 12 − 10 + 6 = 0. So x + 2 is a factor.
True. −2 and −3 multiply to 6 and add to −5.
Factor Theorem.
p(1) = 0.
2 and 3, product 6, sum 5.
(x + 2)(x + 3) = x² + 5x + 6.
p(1) = 1 − 6 + 11 − 6 = 0. By the Factor Theorem, x − 1 is a factor.
पहली चार सर्वसमिकाएँ — प्रश्नावली 2.5 · NCERT 2.6 · Exercise 2.5 · (a+b)²
An identity is an algebraic equality that is true for every value of the variables. The first four:
I. (x + y)² = x² + 2xy + y²
II. (x − y)² = x² − 2xy + y²
III. x² − y² = (x + y)(x − y)
IV. (x + a)(x + b) = x² + (a + b)x + ab
A square of side (a + b) splits into a², ab, ab and b², so (a + b)² = a² + 2ab + b². These work both for products and for factors.
Question: Find 103 × 98 without multiplying directly.
Step 1. 103 = 100 + 3 and 98 = 100 + (−2).
Formula IV: (x + a)(x + b) = x² + (a + b)x + ab. Here x = 100, a = 3, b = −2.
Substitution: 100² + (3 + (−2))×100 + (3)(−2).
Step 2. 10000 + 1×100 + (−6) = 10000 + 100 − 6 = 10094.
Check: 103×100 − 103×2 = 10300 − 206 = 10094.
See 49a² + 70ab + 25b² as (7a + 5b)². First spot the squares and the double product.
For a product without direct multiplication, choose numbers near 100, then use Identity IV.
10-second revision
Do not forget the middle 2xy.
x² + 2·x·3 + 3² = x² + 6x + 9.
False. (x − y)² = x² − 2xy + y². The form x² − y² is a product of two terms.
Difference of squares.
(x + 3)(x − 3).
a + b = −3 + 5 = 2 and ab = −15.
x² + (−3 + 5)x + (−3)(5) = x² + 2x − 15.
True. The two rectangles together make 2ab.
49a² = (7a)², 25b² = (5b)² and 70ab = 2(7a)(5b). So (7a + 5b)² = (7a + 5b)(7a + 5b).
तीन पद और घन की सर्वसमिकाएँ — प्रश्नावली 2.5 · NCERT 2.6 · Exercise 2.5 · cubes
V. (x + y + z)² = x² + y² + z² + 2xy + 2yz + 2zx. It is obtained from (a + b)² by treating (x + y) as one term.
VI. (x + y)³ = x³ + y³ + 3xy(x + y)
VII. (x − y)³ = x³ − y³ − 3xy(x − y)
VIII. x³ + y³ + z³ − 3xyz = (x + y + z)(x² + y² + z² − xy − yz − zx)
If x + y + z = 0, then x³ + y³ + z³ = 3xyz. The expanded form is the right-hand side. The left-hand side is the compact form.
Question: Expand (2x + 1)³.
Formula VI: (x + y)³ = x³ + y³ + 3xy(x + y). Here the first term is 2x and the second is 1.
Substitution: (2x)³ + 1³ + 3(2x)(1)(2x + 1).
Step 1. 8x³ + 1 + 6x(2x + 1).
Step 2. 6x(2x + 1) = 12x² + 6x.
Answer: 8x³ + 12x² + 6x + 1.
In an expansion of three squares, write all of 2xy, 2yz and 2zx. Leaving one out loses marks.
If you see x + y + z = 0, the cubes are directly 3xyz. Open the full Identity VIII only when the sum is not zero.
10-second revision
In VIII the first factor is zero.
x³ + y³ + z³ − 3xyz = 0, so the sum is 3xyz.
True. This is Identity VII.
Twice each pair.
2xy. Likewise 2yz and 2zx.
The sum is 0, so x³ + y³ + z³ = 3xyz = 3×3×(−2)×(−1) = 18. Direct cubes: 27 + (−8) + (−1) = 18. Both agree.
Pick a type. The 30 lesson checks are separate — each lesson has as many as its topic needs. All correct earns mastery ★.
No question is marked as a verified past paper. The BSEB set is a model for practice. CBSE items are CBSE-style, not a copy of any year’s paper.
The exponent −1 is not a whole number.
x + 1/x is not a polynomial. πx + 2 and 5 are polynomials.
Look at the highest power.
The degree is 8.
−b/a = 6/3.
3x = 6, so x = 2.
(x − 2)(x − 3).
p(2) = 4 − 10 + 6 = 0.
a = 1.
The remainder is p(1).
p(−1).
(−1)³ + 1 = 0.
15 and 2.
(3x + 1)(2x + 5).
2xy with y = 4.
2·x·4 = 8x.
Difference of squares.
(x + 4)(x − 4).
Each pair is doubled.
2xy.
The special case of VIII.
3xyz.
The constant 0 is a separate case.
The degree is not defined. Every real number is a zero of it.
True. A non-zero constant has degree 0.
False. A linear polynomial has exactly one zero.
True. That is one direction of the Factor Theorem.
True. This is Identity II.
False. The middle term 2xy is also there.
True. This is Identity VIII.
The highest power.
An example is x² + 1.
The sign is minus.
a ≠ 0.
x − (−3).
a = −3.
Product 12.
3 + 4 = 7 and 3×4 = 12.
The two ab parts of the figure.
Two rectangles.
The product of the three.
The special case of Identity VIII.
7 is constant, 4x+1 linear, x²+1 quadratic, x³−x cubic.
The square has 2xy, the difference has two brackets, the cube has 3xy(x+y), and a zero sum gives 3xyz.
Assertion (A): x − 2 is a factor of p(x) = x² − 4.
Reason (R): p(2) = 0.
Both are true and R explains A.
Assertion (A): The degree of 5 is 0.
Reason (R): The degree of the zero polynomial is also 0.
A is true. R is false. The degree of the zero polynomial is not defined.
Assertion (A): (x + 1)² = x² + 2x + 1.
Reason (R): (x + 1)² = x² + 1.
A is true. R is false, because 2x is missing.
Assertion (A): x + 1/x is a polynomial.
Reason (R): In a polynomial every power of the variable is a whole number.
A is false. R is true. The power of 1/x is −1.
These equations are not results of this maths chapter. This is only practice in filling coefficients. A blank coefficient means 1.
3x²+1 and 7 are polynomials. In 1/x and √x the power is not a whole number.
4x+7 is linear, x²+1 quadratic, 2x³−x cubic. The degree of the zero polynomial is not defined.
The degree is the highest power of the variable, when the leading coefficient is not zero.
x(x − 2) = 0, so the zeroes are 0 and 2.
If p(x) of degree at least 1 is divided by x − a, the remainder is p(a).
x² + 2xy + y².
a = 1. p(1) = 2 − 1 + 4 = 5. The remainder is 5.
−2 and −3 multiply to 6 and add to −5. y² − 2y − 3y + 6 = y(y − 2) − 3(y − 2) = (y − 3)(y − 2).
(100 + 5)(100 + 6) = 100² + (5 + 6)×100 + 5×6 = 10000 + 1100 + 30 = 11130.
Three squares and three double products: 9a² + 16b² + 25c² + 24ab + 40bc + 30ca.
p(x) = (x − a)q(x) + r and r = p(a). Here a = −1 and p(−1) = 0. Long division gives quotient x² − x + 1 and remainder 0. So x + 1 is a factor.
A square of side a+b: an a by a square, a b by b square and two a by b rectangles. The sum is a² + 2ab + b². Here 49a² = (7a)², 25b² = (5b)² and 70ab = 2(7a)(5b). So the factor form is (7a + 5b)².
x³ + y³ + z³ − 3xyz = (x + y + z)(x² + y² + z² − xy − yz − zx). Here 3 + (−2) + (−1) = 0, so x³ + y³ + z³ = 3xyz = 18. Directly, 27 − 8 − 1 = 18.
This model set is for practice. It is not a question from any year annual examination.
A cubic.
The degree of 2x³ − 5 is 3.
x + 5 = 0.
The zero is −5.
10.
2×5 = 10.
True. x + 3x² − 1 is written as 3x² + x − 1.
If p(a) = 0 then (x − a) is a factor, and the converse too. For p(x) = x³ − 1, p(1) = 0, so x − 1 is a factor.
(2x)³ + 1³ + 3(2x)(1)(2x + 1) = 8x³ + 1 + 12x² + 6x = 8x³ + 12x² + 6x + 1. If x + y + z = 0 the right side is 0, so x³ + y³ + z³ = 3xyz.
These are competency-based practice questions. They are not copies of a past paper.
2xy.
2·x·3 = 6x was left out. The full form is x² + 6x + 9.
p(1) = 2 − 3 + 1.
p(1) = 0, so 1 is a zero and x − 1 is a factor.
Assertion (A): x² + 5x + 6 = (x + 2)(x + 3).
Reason (R): The product of 2 and 3 is 6 and their sum is 5.
Both are true and R explains A.
Assertion (A): The degree of the zero polynomial is 0.
Reason (R): A non-zero constant polynomial has degree 0.
A is false. R is true.
x + 1 = x − (−1), so p(−1) = −1 + 1 = 0. The remainder is 0. p(1) = 2 is not the remainder for this divisor.
104 = 100 + 4. (a+b)² = a² + 2ab + b², the four parts of the figure. 100² + 2·100·4 + 4² = 10000 + 800 + 16 = 10816.
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What you learned
| What | Keep this |
|---|---|
| Degree | highest power; 0 if the constant is not zero |
| Zero | p(c) = 0 |
| Remainder | division by x − a leaves p(a) |
| Factor | p(a) = 0 means (x − a) is a factor |
| (a+b)² | a² + 2ab + b² |
| Three cubes | x + y + z = 0 implies x³ + y³ + z³ = 3xyz |
The notes are original writing. The textbook was used only for activity order and numbers. “Verified” will be used only on a question that has a source page.