You may have correctly rewritten $\displaystyle{{\left({144}{b}\right)}}^{{\frac{{1}}{{2}}}}\usepackage{cmbright}\Huge\$ as $\displaystyle{{144}}^{{\frac{{1}}{{2}}}}{{b}}^{{\frac{{1}}{{2}}}}\usepackage{cmbright}\Huge\$ and done some further simplification. However, you simplified $\displaystyle\frac{{b}}{{{b}}^{{\frac{{1}}{{2}}}}}\usepackage{cmbright}\Huge\$ incorrectly. You may have been thinking about division of fractions and multiplied the exponent 1 by $\displaystyle\frac{{2}}{{1}}\usepackage{cmbright}\Huge\$ . The correct way to simplify would be to use the rule: $\displaystyle\frac{{{{x}}^{{a}}}}{{{{x}}^{{b}}}}={{x}}^{{{a}-{b}}}\usepackage{cmbright}\Huge\$