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A rectangle has sides measuring [tex]$2x + 7$[/tex] units and [tex]$5x + 9$[/tex] units.

Part A: What is the expression that represents the area of the rectangle? Show your work. (4 points)

Part B: What are the degree and classification of the expression obtained in Part A? (3 points)

Part C: How does Part A demonstrate the closure property for polynomials? (3 points)

Sagot :

### Part A: Expression for the Area of the Rectangle

To find the area of the rectangle, we need to multiply the expressions for its sides. Given the side lengths:

[tex]\[ \text{Side 1} = 2x + 7 \][/tex]
[tex]\[ \text{Side 2} = 5x + 9 \][/tex]

The area of a rectangle is given by the product of its length and width. Therefore, the area [tex]\(A\)[/tex] is:

[tex]\[ A = (2x + 7) \times (5x + 9) \][/tex]

To expand this expression, we use the distributive property (also known as the FOIL method for binomials):

First, multiply the first terms:
[tex]\[ 2x \cdot 5x = 10x^2 \][/tex]

Next, multiply the outer terms:
[tex]\[ 2x \cdot 9 = 18x \][/tex]

Then, multiply the inner terms:
[tex]\[ 7 \cdot 5x = 35x \][/tex]

Finally, multiply the last terms:
[tex]\[ 7 \cdot 9 = 63 \][/tex]

Now, add all these products together:
[tex]\[ A = 10x^2 + 18x + 35x + 63 \][/tex]

Combine like terms:

[tex]\[ A = 10x^2 + 53x + 63 \][/tex]

So, the expression that represents the area of the rectangle is:
[tex]\[ \boxed{10x^2 + 53x + 63} \][/tex]

### Part B: Degree and Classification of the Expression

The expression obtained for the area of the rectangle is:
[tex]\[ 10x^2 + 53x + 63 \][/tex]

To determine the degree of this polynomial, look at the term with the highest power of [tex]\(x\)[/tex]. Here, the highest power is [tex]\(2\)[/tex] (in the term [tex]\(10x^2\)[/tex]). Therefore, the degree of the polynomial is [tex]\(2\)[/tex].

Polynomials are classified based on their degree:
- A polynomial of degree 1 is called a linear polynomial.
- A polynomial of degree 2 is called a quadratic polynomial.
- A polynomial of degree 3 is called a cubic polynomial, and so on.

Since our polynomial has a degree of 2, it is classified as a quadratic polynomial.

Thus, the degree and classification of the expression [tex]\(10x^2 + 53x + 63\)[/tex] are:
[tex]\[ \text{Degree: } \boxed{2} \][/tex]
[tex]\[ \text{Classification: } \boxed{\text{Quadratic}} \][/tex]

### Part C: Demonstration of the Closure Property

The closure property for polynomials states that the sum, difference, or product of two polynomials is always a polynomial.

In Part A, we multiplied two binomials:
[tex]\[ (2x + 7) \text{ and } (5x + 9) \][/tex]

Each of these binomials is a polynomial. The result of their product, as expanded and simplified, is another polynomial:
[tex]\[ 10x^2 + 53x + 63 \][/tex]

This product is a polynomial itself, confirming that the set of polynomials is closed under multiplication. Therefore, Part A demonstrates the closure property for polynomials because it shows that multiplying two polynomials (in this case, binomials) results in another polynomial.

In conclusion, Part A demonstrates the closure property for polynomials by showing that the product of [tex]\((2x + 7)\)[/tex] and [tex]\((5x + 9)\)[/tex] is the polynomial [tex]\(10x^2 + 53x + 63\)[/tex]. Thus, polynomials are closed under multiplication.