How do I write a polynomial expression to represent the third side of the triangle? I know one side is 2x-3y and the other is x+2y and P=5x+2y? I am lost.

Answer 1

I will assume that P represents the perimeter.

Let the third side be S

S + 2x-3y + x+2y = 5x + 2y
S = 5x+2y - 2x + 3y - x - 2y
= 2x + 3y

check:
What is the sum of (x+2y) + (2x-3y) + (2x+3y) ??