Find the dimensions of a rectangle with perimeter 100 m whose area is as large as possible. (if both values are the same number, enter it into both blanks.)

dA/dx = 100 - 4x & the 2nd derivative is - 4 [i. e. - ve]

so setting dA/dx to zero will give a maxima

100 - 4x = 0

so x = 25 m

in other words, a rectangle with a given perimeter has the maximum area when it is a square