How to find slope. (using a formula)

When turned about its axis of rotation, which shape could have created this three-dimensional object?

Which is a true statement comparing the graphs of x^2/6^2-y^2/8^2 = 1 and x^2/8^2-y^2/6^2 the foci of both graphs are the same points. the lengths of both transverse axes are the same. the directrices of = 1 are horizontal while the directrices of = 1 are vertical. the vertices of = 1 are on the y-axis while the vertices of = 1 are on the x-axis.

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?