I.
$\;a^{\large -x}\,=\,-\,a^{\large x}, \,\forall\,x\,\in\;\mathbb{R}$
II.
$\;2a^{\large x}\,+\,\,a^{\large x}\,=\,3\,\centerdot\,a^{\large x}, \,\forall\,x\,\in\;\mathbb{R}$
III.
$\;a^{\large x}\,\centerdot\,a^{\large x}\,=\,\,a^{\large x^2}, \,\forall\,x\,\in\;\mathbb{R}$
