Maximum area of a 3 sided rectangle with a 300 ft. perimeter?

I think I know what you mean: A rectangular region surrounded on three sides by 300 ft of fence.

         no fence

       |                |

     y |                | y

       |_________|

               x

     x + 2y = 300   ...   perimeter equation

             x = 300 – 2y

  Area = x • y

  Area = (300 – 2y) • y   ...   substituted for "x"

  Area = -2y² + 300y   ...   quadratic of the form: Area = ay² + by + c

The maximum in Area is located at the vertex of the quadratic:

      Yvertex = -b ⁄ (2a)

      Yvertex = -300 ⁄ (2•(-2))

      Yvertex = 75 ft

             x = 300 – 2y   ...   perimeter equation

             x = 300 – 2(75)

             x = 150 ft

  Area = x • y

  Area = (150) • (75)

  Area = 11250 ft²   ...   maximum area

there is no such thing as a "3 sided rectangle".

a rectangle has FOUR sides.

a TRIANGLE has 3 sides.

If it has three sides then it is a triangle NOT a rectangle.

for ,maximum area a triangle is equilateral so each side is 100'.

You do the math for area.

<without doing a ton of work>

Ah, but you want someone ELSE to, eh?

Yes