What is the length of the missing side of the quadrilateral shown if the perimeter is 5x^2+2x+1

X=length of a side.

y=lenght of the missnt side.

perimeter of this quadrilateral=2x+2y

perimeter or this quadrilateral=5x²+2x+1

Therefore:

5x²+2x+1=2x+2y

2y=5x²+2x-2x+1

2y=5x²+1

y = (5x²+1) / 2

Answer:

y=length of the missing side.

y = (5x²+1) / 2