Answer:
Part A:
To find the total length of the two sides of the triangle, we need to add Side 1 and Side 2:
Side 1: 3x² - 4x - 1
Side 2: 4x - x² + 5
Total length: (3x² - 4x - 1) + (4x - x² + 5)
Simplifying and combining like terms, we get:
Total length: -x² + 7x + 4
Therefore, the total length of the two sides of the triangle is -x² + 7x + 4.
Part B:
To find the length of the third side of the triangle, we need to subtract the sum of Side 1 and Side 2 from the perimeter of the triangle:
Length of Side 3 = Perimeter - (Side 1 + Side 2)
Length of Side 3 = (5x³ - 2x² + 3x - 8) - (3x² - 4x - 1 + 4x - x² + 5)
Simplifying and combining like terms, we get:
Length of Side 3 = 2x³ - 2x² + 7x - 12
Therefore, the length of the third side of the triangle is 2x³ - 2x² + 7x - 12.
Part C:
The answers for Part A and Part B show that the polynomials are closed under addition and subtraction. The sum of Side 1 and Side 2 is a polynomial (-x² + 7x + 4), and the difference between the perimeter of the triangle and the sum of Side 1 and Side 2 is also a polynomial (2x³ - 2x² + 7x - 12). In both cases, the result is a polynomial, which means that the set of polynomials is closed under addition and subtraction.