Chapter 5: Problem 60
Factor completely. See Examples 1 through \(9 .\) $$ x^{2}-18 x+81-y^{2} $$
Short Answer
Expert verified
The expression factors to \((x-9+y)(x-9-y)\).
Step by step solution
01
Identify the Type of Expression
The given expression is \( x^2 - 18x + 81 - y^2 \). Notice the structure: it comprises a quadratic trinomial \( x^2 - 18x + 81 \) and a \( y^2 \) term. This can be converted into a difference of squares.
02
Factor the Quadratic Trinomial
The expression \( x^2 - 18x + 81 \) is a perfect square trinomial. It can be rewritten as \( (x-9)^2 \) since \((x-9)(x-9) = x^2 - 18x + 81\). Check by expanding: \[(x-9)^2 = x^2 - 18x + 81.\]
03
Express as a Difference of Squares
Now substitute the quadratic trinomial with its factored form: \( (x-9)^2 - y^2 \). This expression is now in the form of a difference of squares: \[ (A)^2 - (B)^2, \] where \( A = (x-9) \) and \( B = y \).
04
Factor the Difference of Squares
The difference of squares \( (A)^2 - (B)^2 \) can be factored using the formula \[ A^2 - B^2 = (A + B)(A - B). \] So, \[(x-9)^2 - y^2 = ((x-9) + y)((x-9) - y).\]
05
Write the Final Factored Expression
Write down the factored form of the initial expression: \((x-9+y)(x-9-y)\). This is the completely factored form of the original expression \(x^2 - 18x + 81 - y^2\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Difference of Squares
The difference of squares is a crucial method in factoring polynomials. It applies when you have two terms, both squares, separated by a subtraction sign. Let's break it down further. The general form is \( a^2 - b^2 \), where both \( a \) and \( b \) are any expressions that can be squared.
To factor a difference of squares, use the identity: \( a^2 - b^2 = (a + b)(a - b) \). This formula is extremely useful because it simplifies expressions into a product of two binomials. The expression \( (x-9)^2 - y^2 \) fits this pattern.
To factor a difference of squares, use the identity: \( a^2 - b^2 = (a + b)(a - b) \). This formula is extremely useful because it simplifies expressions into a product of two binomials. The expression \( (x-9)^2 - y^2 \) fits this pattern.
- Let \( A = x - 9 \), the first square.
- Let \( B = y \), the second square.
Quadratic Trinomials
A quadratic trinomial is a polynomial expression with three terms, shaped generally like \( ax^2 + bx + c \). These are common in algebra and mastering their factoring is essential. The key is learning to transform them into binomials, like \((x - p)(x - q)\).
In this case, consider \( x^2 - 18x + 81 \). It looks intimidating, but it is designed as a "perfect square trinomial."
In this case, consider \( x^2 - 18x + 81 \). It looks intimidating, but it is designed as a "perfect square trinomial."
- The perfect squares are important. Notice the squares: \( x^2 \) and \( 81 = 9^2 \).
- The middle term, \(-18x\), is twice the product of \( x \) and \( 9 \). This confirms it is a perfect square trinomial.
Perfect Square Trinomials
Perfect square trinomials are a special type of quadratic expressions. They arise from squaring a binomial, which results in a neat, predictable pattern. The general form for perfect square trinomials is \((a \,\pm b)^2 = a^2 \pm 2ab + b^2\).
In our example, \( x^2 - 18x + 81 \) is a perfect square trinomial. It perfectly matches the pattern \((x-9)^2 = x^2 - 18x + 81\). Here's why:
In our example, \( x^2 - 18x + 81 \) is a perfect square trinomial. It perfectly matches the pattern \((x-9)^2 = x^2 - 18x + 81\). Here's why:
- First term: \( x^2 \) is \( (x)^2 \).
- Middle term: \(-18x\) is \(-2(x)(9)\), fitting the \(-2ab\) part of the pattern.
- Last term: \( 81 \) is \( (9)^2 \).