Question 2 (Essay Worth 10 points)
(07.03, 07.04 MC)
Part A: The area of a square is (4x2 − 12x + 9) square units. Determine the length of each side of the square by factoring the area expression completely. Show your work. (5 points)
Part B: The area of a rectangle is (16x2 − 9y2) square units. Determine the dimensions of the rectangle by factoring the area expression completely. Show your work. (5 points)
Answers
Answer:
Area = side²
If Area = 4x² + 12x + 9, then the side is the √(4x² + 12x + 9)
Let’s factor 4x² + 12x + 9
What two numbers multiply to be 36 (which came from 4 * 9) add up to be 12?
6 and 6 are the two numbers, because 6 * 6 = 36, and 6 + 6 = 12.
We can break 4x² + 12x + 9 into (4x² + 6x) + (6x + 9)
Factor 4x² + 6x, the greatest common factor is 2x, so the 2x goes on the outside, leaving us with 2x + 3 on the inside, so that gives us 2x * (2x + 3).
Factor 6x + 9, the greatest common factor is 3, so the 3 goes on the outside, leaving us with 2x + 3 on the inside, that gives us 3 * (2x + 3).
Now we have the 4x² + 12x + 9 written as 2x (2x + 3) + 3 (2x + 3). Since we now have a common factor, 2x + 3, we can combine them by adding 2x (2x + 3) + 3 (2x + 3) as like terms, so we now have (2x + 3) * (2x + 3).
We can simplify (2x + 3)(2x + 3) into (2x + 3)².
There. The simplest factored form of 4x² + 12x + 9 is (2x + 3)²
Ok, the Area = (2x + 3)²
Let’s solve for the side
(2x + 3)² = side²
square root both sides and take the positive root
side = √(2x + 3)²
side = 2x + 3
The side length is: 2x + 3 units
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