Dylan uses the expressions [tex](x^2 - 2x + 8)[/tex] and [tex](2x^2 + 5x - 7)[/tex] to represent the length and width of his bedroom. Which expression represents the area ( [tex]A[/tex] ) of Dylan's room?

A. [tex]2x^4 - 10x^2 - 56[/tex]
B. [tex]2x^4 + 10x^2 + 56[/tex]
C. [tex]2x^4 + x^3 - x^2 + 54x - 56[/tex]
D. [tex]2x^4 + 9x^3 + 33x^2 + 54x + 56[/tex]



Answer :

To determine the area of Dylan's bedroom, we need to multiply the expressions representing the length and width. Let's break it down step-by-step:

1. Identify the expressions:
- Length of the room: [tex]\( x^2 - 2x + 8 \)[/tex]
- Width of the room: [tex]\( 2x^2 + 5x - 7 \)[/tex]

2. Multiply the expressions:
To find the area, we use the distributive property (also known as the FOIL method for binomials) to multiply these polynomials:

[tex]\[ \begin{aligned} & (x^2 - 2x + 8)(2x^2 + 5x - 7) \\ & = x^2 \cdot (2x^2 + 5x - 7) - 2x \cdot (2x^2 + 5x - 7) + 8 \cdot (2x^2 + 5x - 7) \\ &= (x^2 \cdot 2x^2) + (x^2 \cdot 5x) + (x^2 \cdot -7) \\ &\quad - (2x \cdot 2x^2) - (2x \cdot 5x) - (2x \cdot -7) \\ &\quad + (8 \cdot 2x^2) + (8 \cdot 5x) + (8 \cdot -7) \\ &= 2x^4 + 5x^3 - 7x^2 - 4x^3 - 10x^2 + 14x + 16x^2 + 40x - 56 \end{aligned} \][/tex]

3. Combine like terms:
Now we combine the terms with the same degree:

[tex]\[ \begin{aligned} & 2x^4 + (5x^3 - 4x^3) + (-7x^2 - 10x^2 + 16x^2) + (14x + 40x) - 56 \\ & = 2x^4 + x^3 - x^2 + 54x - 56 \end{aligned} \][/tex]

4. Compare with options given:
After multiplying and simplifying the expression, the resulting polynomial is:

[tex]\[ 2x^4 + x^3 - x^2 + 54x - 56 \][/tex]

By examining the given options, we find that this expression matches exactly with one of the options provided:

[tex]\[ \boxed{2x^4 + x^3 - x^2 + 54x - 56} \][/tex]

Therefore, the expression that represents the area of Dylan's room is [tex]\(2x^4 + x^3 - x^2 + 54x - 56\)[/tex].