1,-2,4,-8 what is the rule for the sequence ?

You multiply by -2 each time.

1*-2= -2

-2*-2= 4

4*-2= -8

Skew lines(segments) are lines(segments) in 3 dimensions that do not intersect the given segment and are not parallel to it.  ae, bf, eg, and fh are your skew segments.  i hope that : )