The amplitude of $\displaystyle{y}={a}{\sin{{b}}}{x}\usepackage{cmbright}\Huge\$ is given by $\displaystyle{\left|{a}\right|}\usepackage{cmbright}\Huge\$ . So the amplitude of $\displaystyle{y}=-{4}{\sin{{2}}}{x}\usepackage{cmbright}\Huge\$ is $\displaystyle{\left|-{4}\right|}={4}\usepackage{cmbright}\Huge\$ .