The ornamental design for a tabletcomputer, as shown and described.
FIG. 1 is a perspective view of a tablet computer showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is another perspective view thereof, showing the tablet computer in an open position; and,
FIG. 9 is a right side elevation view showing the tablet computer in an open position and showing the tablet portion detached from the keyboard portion.
The broken lines depict portions of the tablet computer that form no part of the claimed design.