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About Expansions — Class 9 ICSE

Use standard algebraic identities to expand expressions and simplify complex products. This topic is part of the ICSE Class 9 mathematics syllabus (chapter: Chapter 3). On this page you can practice 60 questions across three difficulty levels — 20 easy, 20 medium, and 20 hard — each with a visual step-by-step solution, plus a timed 35-question mastery test with a live leaderboard. Worked examples and sample questions from the topic are below.

What you'll learn in Expansions

  • Introduction to Expansions: The Square of a Binomial
  • Expanding with Subtraction and Difference of Squares
  • Expanding Trinomials: The $(x+a)(x+b)$ Identity
  • Advanced Applications: Cube Identities
  • Summary, Connections, and Exam Preparation

Interactive lesson · about 15 minutes · checkpoint question after every unit

Expansions — solved examples for Class 9 ICSE

Example 1easy

Ravi was asked to expand the expression (3x + 2y)². He wrote the expansion as 9x² + 4y². Which of the following statements correctly identifies the mistake in Ravi's expansion?
  1. A)Ravi used the identity (a - b)² instead of (a + b)².
  2. B)Ravi squared the constant terms incorrectly; 3² should be 6 and 2² should be 4.
  3. C)Ravi forgot to include the middle term, 2ab, from the identity (a + b)².
  4. D)Ravi incorrectly identified 'a' as 3x and 'b' as 2y.

Step-by-step solution

  1. The correct algebraic identity for (a + b)² is a² + 2ab + b².
  2. In the expression (3x + 2y)², 'a' is 3x and 'b' is 2y.
  3. So, (3x + 2y)² = (3x)² + 2(3x)(2y) + (2y)² = 9x² + 12xy + 4y².
  4. Ravi's expansion 9x² + 4y² only includes the a² and b² terms, missing the 2ab term (which is 12xy).

Answer: Ravi forgot to include the middle term, 2ab, from the identity (a + b)².

Example 2medium

Simplify the expression: (5x + 3y)² - (5x - 3y)².
  1. A)10x² + 18y²
  2. B)60xy
  3. C)25x² - 9y²
  4. D)0

Step-by-step solution

  1. Let a = (5x + 3y) and b = (5x - 3y). The expression is in the form a² - b².
  2. Using the identity a² - b² = (a - b)(a + b):
  3. ( (5x + 3y) - (5x - 3y) ) × ( (5x + 3y) + (5x - 3y) )
  4. (5x + 3y - 5x + 3y) × (5x + 3y + 5x - 3y) = (6y) × (10x) = 60xy.

Answer: 60xy

Example 3hard

Simplify the expression: (x² + y² - z²)² - (x² - y² + z²)².
  1. A)4x²(y² - z²)
  2. B)4y²(x² - z²)
  3. C)8x²y²
  4. D)8x²z²

Step-by-step solution

  1. Let A = x² + y² - z² and B = x² - y² + z².
  2. The expression is in the form A² - B², which expands to (A - B)(A + B).
  3. Calculate A - B: (x² + y² - z²) - (x² - y² + z²) = x² + y² - z² - x² + y² - z² = 2y² - 2z² = 2(y² - z²).
  4. Calculate A + B: (x² + y² - z²) + (x² - y² + z²) = x² + y² - z² + x² - y² + z² = 2x².
  5. Multiply (A - B)(A + B): 2(y² - z²) × 2x² = 4x²(y² - z²).

Answer: 4x²(y² - z²)

Practice questions on Expansions

  1. Q1.easy

    Which of the following statements is TRUE regarding algebraic expansions?
    1. A)(p - q)² is always equal to p² - q².
    2. B)(a + b)(a - b) is always equal to a² - b².
    3. C)(x + y)² is equal to x² + y².
    4. D)The expansion of (m + n + o)² has only three terms.
    Show answer

    Answer: (a + b)(a - b) is always equal to a² - b².

    Hint: Carefully recall the standard algebraic identities. There's a common misconception in some of the options.

  2. Q2.easy

    Expand the expression (x - 7)(x + 3) using a suitable algebraic identity.
    1. A)x² - 4x - 21
    2. B)x² + 4x - 21
    3. C)x² - 4x + 21
    4. D)x² + 4x + 21
    Show answer

    Answer: x² - 4x - 21

    Hint: Consider the identity (x + a)(x + b) and pay close attention to the signs of 'a' and 'b'.

  3. Q3.easy

    If the product of two expressions is 25m² - 49n², and one of the expressions is (5m + 7n), what is the other expression?
    1. A)(5m + 7n)
    2. B)(25m - 49n)
    3. C)(5m + 49n)
    4. D)(5m - 7n)
    Show answer

    Answer: (5m - 7n)

    Hint: Recognize the form of the product: it's a difference of two squares. Which identity results in such a form?

  4. Q4.medium

    If x + 1/x = 5, what is the value of x² + 1/x²?
    1. A)23
    2. B)25
    3. C)27
    4. D)29
    Show answer

    Answer: 23

    Hint: Square both sides of the given equation (x + 1/x = 5) and then simplify.

  5. Q5.medium

    Expand the expression (2x - 0.5)(2x + 1.5).
    1. A)4x² + 2x - 0.75
    2. B)4x² + x - 0.75
    3. C)4x² - x - 0.75
    4. D)4x² + 2x + 0.75
    Show answer

    Answer: 4x² + 2x - 0.75

    Hint: Use the identity (y + a)(y + b) = y² + (a + b)y + ab, where y = 2x.

  6. Q6.medium

    Rohan was asked to expand (p - q + r)². He wrote the expansion as p² + q² + r² - 2pq + 2qr - 2pr. Identify if his expansion is correct or incorrect, and if incorrect, state the correct term for 2qr.
    1. A)Correct
    2. B)Incorrect, 2qr should be -2qr
    3. C)Incorrect, 2qr should be +2qr
    4. D)Incorrect, 2qr should be 2pq
    Show answer

    Answer: Incorrect, 2qr should be -2qr

    Hint: Recall the identity (a + b + c)² = a² + b² + c² + 2ab + 2bc + 2ca. Pay close attention to the signs of b and c in the given expression.

  7. Q7.hard

    If x + 1/x = 5, find the value of x⁴ + 1/x⁴.
    1. A)527
    2. B)529
    3. C)531
    4. D)533
    Show answer

    Answer: 527

    Hint: Start by squaring the given expression x + 1/x = 5 to find x² + 1/x². Then, square the result again.

  8. Q8.hard

    Rahul was asked to expand (3a - 2b - c)². He wrote his solution as 9a² + 4b² + c² - 12ab - 4bc - 6ca. Which term in his expansion is incorrect?
    1. A)9a²
    2. B)4b²
    3. C)-12ab
    4. D)-4bc
    Show answer

    Answer: -4bc

    Hint: Recall the identity (x + y + z)² = x² + y² + z² + 2xy + 2yz + 2zx. Pay close attention to the signs of y and z when calculating the 2yz term.

  9. Q9.hard

    If 25x² + 4y² - 20xy is equivalent to (Ax + By)², where A and B are integers, what is the value of A + B?
    1. A)3
    2. B)7
    3. C)13
    4. D)Both 3 and -3
    Show answer

    Answer: Both 3 and -3

    Hint: Recognize the perfect square trinomial form a² - 2ab + b². Remember that (X - Y)² is the same as (Y - X)².

These are 9 of the 60 questions available for Expansions. Start practicing above to unlock visual solutions, AI coaching, and the topic leaderboard — completely free.