Mistake.
Do RM parallel PQ, across BB 1 to m; Make PN parallel to QR and pass through A 1D 1 in n.
The pentagon formed by five points PQRMN is the section.
The best way to find a section in a cube is to do parallel operation and find the intersection point of each edge.
④ the line segments EF and GH move on the sides A 1B 1 and CC 1 respectively, and EF+GH= 1, then the triangular pyramid e
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The maximum volume of FGH is112.
Let g be above h, then E-FGH=G-EFC 1 minus H-EFC 1.
= 1/3 * EF * GC 1- 1/3 * EF * HC 1
= 1/3*EF*GH
EF+GH= 1, then the maximum value of EF*GH = 1/4.
This item is correct.