Thank you to Meg for sending us these great
diagrams! Did you make the shapes in the same
way?
Here is a diagram showing how the original square should be
cut.
These pieces can be arranged to make a triangle like this:

The parallelogram can be made like this:

The square can be made as shown in the first diagram.
Well done Meg!
If you enjoyed this puzzle, you might like
to look at some of the Tangram puzzles on this site, for
example Tangram
or Tangrams - World of Tan.