Bernard Lemaire still wants you to find a 5-piece dissection of the cross to a square.
The first hint led you to learn that the square will be 7 on a side. But how should you arrange a large piece from the cross inside the square? Try overlaying the square on top of the cross, so that all of the top arm of the cross and all of the right arm of the cross will be within the square.
But you shouldn't make this piece from the cross as large as possible, because then the remaining pieces can't be cut conveniently to fill in the voids. So you need to play around with how to cut off the lower arm and the left arm of the cross. Try working with this idea for a while, until you solve the puzzle or need a third hint.
Copyright 2002, Greg N. Frederickson.