Question 1121334
It would be a square, so each side is 10/4 = 2.5,  thus the area is {{{2.5^2 = highlight( 6.25 ) }}} sq units
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Proof (using Calculus):
        Let x = length 
        Then  w = width = (10 - 2x) / 2

Area,  A,  is  {{{ A = x*w = x (10-2x)/2 = 5x-x^2 }}}

{{{ dA/dx = 5-2x  }}}

5-2x = 0  —>  x = 5/2 = 2.5

Since {{{ dA^2/d^2x = -4/2 = -2 }}} the curve is concave down so the value is a maximum.

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Without Calculus, you can graph the function and compute values by hand.

{{{ graph(300,300, -5,5,-5,10, grid(1), 5x-x^2) }}}