Algebraic Expansion: Multiplying Polynomials, Binomial Products, and Special Inspection Identities
In this lesson, we master expanding brackets and multiplying algebraic expressions. We begin by multiplying a monomial by a polynomial using the 'Distributive Property': the exterior term multiplies every term inside parentheses sequentially: a(b + c) = ab + ac. Next, we explore binomial multiplication (a + b)(c + d), where every term in the first binomial multiplies every term in the second, and resulting like terms are combined. The pinnacle of this lesson is 'Special Products by Inspection'—celebrated algebraic identities that eliminate intermediate steps: First: the Square of a Binomial: (a ± b)² = (first)² ± 2(first)(second) + (second)² = a² ± 2ab + b², producing a perfect square trinomial. Second: the Product of the Sum and Difference of Two Terms: (a + b)(a - b) = (first)² - (second)² = a² - b², producing a Difference of Two Squares where the middle term vanishes completely.
1. Distributive Expansion & Binomial Multiplication
Multiplying polynomials systematically:
- Term by Expression: 3x(2x - 5) = (3x × 2x) - (3x × 5) = 6x² - 15x.
- Binomial by Binomial: (x + 3)(x + 5)
• Product of firsts: x × x = x²
• Sum of extremes + means: (5x + 3x) = 8x
• Product of lasts: 3 × 5 = 15
• Result = x² + 8x + 15.
2. Special Inspection Identities
Instant expansion formulas:
- Square of a Binomial: (a ± b)² = a² ± 2ab + b²
• (x + 4)² = x² + 2(x)(4) + 16 = x² + 8x + 16.
• (2x - 3)² = (2x)² - 2(2x)(3) + 3² = 4x² - 12x + 9. - Difference of Two Squares: (a + b)(a - b) = a² - b²
• (x + 5)(x - 5) = x² - 25 (no middle term!).
• (3x - 2)(3x + 2) = 9x² - 4.
Special Product Workshop:
(a) Square of binomial: x² - 2(x)(6) + 6² = x² - 12x + 36.
(b) Difference of squares: (2x)² - (7)² = 4x² - 49.
Write 101 as (100 + 1)²:
(100 + 1)² = 100² + 2(100)(1) + 1² = 10000 + 200 + 1 = 10201.
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