how can u make a box with 3 lines?

Answer 1

Draw three lines converging at the same point and say it's a close-up perspective drawing of a cube.

Draw a triangle and call it a three-sided box. (You never said what shape the box should be.)

Answer 2

make a triangular box if it is 2-d.

if it is 3d...you can't

Answer 3

MAKE ONE LINE CURVE