E 4) In the diagram below, the dimensions of the large rectangle are (3x-1) by (3x+7) units. The dimensions of the cut-out rectangle are x by (2x+5) units. Which choice expresses the area of the shaded region, in Square units?

Answer:
Option (D)
Step-by-step explanation:
Area of a rectangle = Length × width
Area of large rectangle = (3x - 1)(3x + 7) square units
= (9x² + 21x - 3x - 7)
= 9x² + 18x - 7
Area of small rectangle = (2x + 5)x
= (2x² + 5x) square units
Area of the shaded region = Area of large rectangle - Area of small rectangle
= (9x²+ 18x - 7) - (2x² + 5x)
= (9x² - 2x²) + (18x - 5x) - 7
= (7x² + 13x - 7) square units
Therefore, Option (D) will be the correct option.
The expression that represents the area of the shaded region is:[tex]7x\² + 13x - 7[/tex]
The dimension of the big rectangle is given as:
So, the area of the rectangle is:
[tex]Area = Length \times Width[/tex]
[tex]Area= (3x - 1) \times (3x + 7)[/tex]
Expand
[tex]Area = 9x\² + 21x - 3x - 7[/tex]
[tex]Area = 9x\² + 18x - 7[/tex]
The dimension of the small rectangle is given as:
So, the area of the rectangle is:
[tex]Area = Length \times Width[/tex]
[tex]Area= (2x + 5) \times x[/tex]
Expand
[tex]Area = 2x\² + 5[/tex]
The area of the shaded region is the difference between the area of the big and small rectangles.
So, we have:
[tex]Area = (9x\²+ 18x - 7) - (2x\² + 5x)[/tex]
Expand, and collect like terms
[tex]Area = 9x\²- 2x\² + 18x -5x- 7[/tex]
[tex]Area = 7x\² + 13x - 7[/tex]
Hence, the area of the shaded region is [tex]7x\² + 13x - 7[/tex]
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