Since $\displaystyle{x}={2}\usepackage{cmbright}\Huge\$ , $\displaystyle\frac{{1}}{{4}}{{x}}^{{4}}-\frac{{1}}{{2}}{{x}}^{{2}}=\frac{{1}}{{4}}\cdot{{2}}^{{4}}-\frac{{1}}{{2}}\cdot{{2}}^{{2}}=\frac{{1}}{{4}}\cdot{16}-\frac{{1}}{{2}}\cdot{4}={4}-{2}={2}\usepackage{cmbright}\Huge\$ .