Just do it.
Your answer.
gives and so dm.
The poster should be approximately by dm.
is uniform with , so so that .
The length of the ladder is .
Using differentiation you now determine the minimum of .
You find a minimal length of m.
Denote the base of the isosceles triangle by , then the edges are each.
The area is .
gives and so .
So the three edges are all cm.
Make a sketch of the situation.
gives and so that .
If is .
gives and so . Extrema max. and min. .
gives .
There are no solutions if and also if there are no extrema.
and gives .
The length of is .
is minimal if is minimal.
if .
The minimal length of line segment is .
The area of rectangle is .
als .
The maximum area is .