how do you write a quadratic equation for area

Question

A rectangular corral is to be built by stringing an electric fence as with Y feet for a side and X feet for each of the two sides perpendicular to the river. The total length of fence is to be 900 feet. what is the quadratic equation that represents area of the corral and what value of X makes the maximum area and what is the area?

Answer 1

y = 900 - 2x

A = x(900 - 2x)

A = -2x² + 900x

 

Complete the square. The ordered pair naming the vertex gives the value of x and the maximum area.