(1) For the equation $8 x^{2}-m x+(m-6)=0$ about $x$, when $m$ takes what range of values, the two roots of the equation (1) are both positive; (2) are both negative; (3) have opposite signs?
(1) (1) $6<m \leqslant 8$ or $m \geqslant 24$
(2) $m$ does not exist
(3) $m<6$