Dear forum members,
A problem asks me to show that a rectangle of constant area A has a minimal perimeter when the rectangle is a square.
I make the equation for the area and differentiate it with respect to x.
Solving for the zero points
At this stage, am I allowed to substitute A=xh into the equation and solve it as
x=0 or x=h
or should I solve it as
because evidently the answer is different .
Please help me, I am really confused.
Thank you in advance.