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Method A3

In this movie F starts at A and moves towards and then beyond C and then back to and beyond A.

It is worth PAUSING the movie at various locations.

What happens in the movie at the instant when F coincides with C ? Why?
When F moves beyond C, it turns out that FG is still parallel to DE, but we may have to modify our proof.
Similarly, when F moves beyond A, it turns out that FG is still parallel to DE, but we may again have to modify our proof (the Angles in the same segment theorem is useful here).

On the next page we look in more detail at the situation where F is on CA produced, but from a new perspective.
However, you might first want to use this JAVA worksheet to explore the configuration in a more interactive way.