Mathematical signs
Use definition of division. I do the first one. $\displaystyle a|1 \implies 1 = ab \implies a=\pm 1$.
And second one $\displaystyle a|b \implies a = bc$, $\displaystyle b|a\implies b = ad$.
Thus, $\displaystyle a = bc = adb \implies 1 = bd \implies d = \pm 1$ (assuming $\displaystyle a\not = 0$).