(1) (x-h)^2/a^2 - (y-k)^2/b^2 = 1
vs.
(2) -(x-h)^2/a^2 + (y-k)^2/b^2 = 1
Notice (2) has a minus sign on the "h" term. "h" stands for hourglass and minus means NOT--so (1) is hourglass type, resembling hourglass silhouette and (2) is NON-hourglass type
(1) (x-h)^2/a^2 - (y-k)^2/b^2 = 1
vs.
(2) -(x-h)^2/a^2 + (y-k)^2/b^2 = 1
Notice (2) has a minus sign on the "h" term. "h" stands for hourglass and minus means NOT--so (1) is hourglass type, resembling hourglass silhouette and (2) is NON-hourglass type