Using the graph you find: min. en max. .
gives . Using the graph you find: .
Line through and is . This line can only be tangent to the graph in or . Now and . So line is a tangent in .
Assume the width is cm, then the length is cm. And so .
from this it follows that the length of the ribbon is given by: .
gives and so cm.
Using the graph of or a sign scheme of you see that has a minimum for . The dimensions of the box are: (in cm).
Just do it.
when . Using the graph you find: min. .
does not change signs for .
The maximum of the generated power is Watt.