Texas Instruments TI-83 PLUS - Manual (Page 222)

TI-83 Plus Draw Instructions 219
Drawing a Line Segment from the Home Screen or a Program
Line( also draws a line segment between the coordinates ( X1,Y1 ) and
( X2,Y2 ). The values may be entered as expressions.
Line( X1,Y1,X2,Y2 )
To erase a line segment, enter Line( X1,Y1,X2,Y2, 0)