PLZ HELP
I will mark Brainliest
I am not to sure about answering it.

The lengths of two sides of a triangle are shown.
Side 1: 3x^2 − 2x − 1
Side 2: 9x + 2x^2 − 3

The perimeter of the triangle is 5x^3 + 4x^2 − x − 3.

Part A: What is the total length of the two sides, 1 and 2, of the triangle? Show your work.(4 points)

Part B: What is the length of the third side of the triangle? Show your work. (4 points)

Part C: Do the answers for Part A and Part B show that the polynomials are closed under addition and subtraction? Justify your answer. (2 points)

Thank you to anyone who answers correctly!

Part A:

To find the total length of the two sides you want to add them together:

(3x^2-2x-1)+(9x+2x^2-2)= you want to combine all like terms

3x^2+2x^2=5x^2, you add your coefficients and keep the exponents the same

-2x+9x=7x, you would combine like terms

-1-2=-3, you would subtract according to Keep, Change, Change

You now have:

5x^2+7x-3= Sides A+B

5x^2+7x-3

Part B:

To find the length of the third side you want to take the perimeter of the triangle and subtract it from our answer in part A

(5x^3+4x^2-x-3)-(5x^2+7x-3)

When subtraction polynomials we want to change the subtraction sign to addition and change the signs of the other number to the opposite sign to prevent making mistakes from subtraction, so you're new equation will look like this:

(5x^3+4x^2-x-3)+(-5x^2-7x+3)

Now we add all like terms again

5x^3, doesn't combine with any others so we leave it the same

4x^2-5x^2=-x^2, subtract them but remember to keep the exponents the same

-x-7x=-8x, again subtract terms but keep variable

-3+3=0, they cancel out so we don't have to worry about putting anything for this one

So now we are left with

5x^3-x^2-8x as our length for the third side

Third side equals 5x^3-x^2-8x

Part C:

For part A we added to get the total of sides B and A

For part B we subtracted the total perimeter from the total lengths of B and A, to figure out what C equals

Hope this helps ;)

16.9 times 2.85

step-by-step explanation: