Select the expression that is equivalent to the given polynomial.

[tex]x^4 - 81[/tex]

A. [tex](x-3)(x-3)(x+3i)(x-3i)[/tex]
B. [tex](x-3)(x-3)(x-3i)(x-3i)[/tex]
C. [tex](x+3)(x+3)(x+3i)(x+3i)[/tex]
D. [tex](x+3)(x-3)(x+3i)(x-3i)[/tex]



Answer :

To solve the given problem, [tex]\( x^4 - 81 \)[/tex], we need to factorize the polynomial completely. Let's start by recognizing the pattern in the polynomial.

1. Recognize the Structure: Difference of Squares

The expression [tex]\( x^4 - 81 \)[/tex] is a difference of squares because it can be written as:
[tex]\[ x^4 - 81 = (x^2)^2 - 9^2 \][/tex]
According to the difference of squares formula, [tex]\( a^2 - b^2 = (a + b)(a - b) \)[/tex]:
[tex]\[ (x^2)^2 - 9^2 = (x^2 + 9)(x^2 - 9) \][/tex]

2. Factorize Further: [tex]\( x^2 - 9 \)[/tex]

Next, we can further factorize [tex]\( x^2 - 9 \)[/tex]. Noting that [tex]\( x^2 - 9 \)[/tex] is again a difference of squares:
[tex]\[ x^2 - 9 = (x + 3)(x - 3) \][/tex]

3. Handle [tex]\( x^2 + 9 \)[/tex]

The term [tex]\( x^2 + 9 \)[/tex] can also be factorized using complex numbers because it can be rewritten as:
[tex]\[ x^2 + 9 = x^2 + (3i)^2 = (x + 3i)(x - 3i) \][/tex]
where [tex]\( i \)[/tex] is the imaginary unit satisfying [tex]\( i^2 = -1 \)[/tex].

4. Combine All Factors

Bringing together all these factors, the complete factorization of [tex]\( x^4 - 81 \)[/tex] is:
[tex]\[ x^4 - 81 = (x^2 + 9)(x^2 - 9) = (x + 3i)(x - 3i)(x + 3)(x - 3) \][/tex]

This factorization matches the polynomial factorization provided in Option D:
[tex]\[ (x + 3)(x - 3)(x + 3i)(x - 3i) \][/tex]

Therefore, the correct answer is
[tex]\[ \boxed{D} \][/tex]