These two graphs do have the same shape and they will be mirror images, but $\displaystyle{y}=-{{2}}^{{x}}\usepackage{cmbright}\Huge\$ has only negative values. Therefore the graph of $\displaystyle{y}=-{{2}}^{{x}}\usepackage{cmbright}\Huge\$ will be entirely below the x-axis. These graphs will be reflections across the x-axis and not the y-axis, unlike the graphs shown.