The expression 6x-8 represents the perimeter of a shape in terms of the length of one of its sides, while the expression 4(1.5x-2) represents the perimeter of the same shape in terms of the length of its diagonals. Therefore, the expression 4(1.5x-2) provides additional information about the shape that is not contained in the expression 6x-8. Specifically, the expression 4(1.5x-2) tells us that the length of each diagonal of the shape is equal to 1.5 times the length of one of its sides minus 2. This information allows us to determine the lengths of the diagonals of the shape, which is not possible with the information provided by the expression 6x-8.