Correct. By applying the formula $\displaystyle{{\left({a}-{b}\right)}}^{{2}}={{a}}^{{2}}-{2}{a}{b}+{{b}}^{{2}}\usepackage{cmbright}\Huge\$ , you successfully found the square of $\displaystyle{7}{{x}}^{{3}}-{9}{{x}}^{{2}}\usepackage{cmbright}\Huge\$ .