You may have correctly rewritten $\displaystyle-{7}{x}\usepackage{cmbright}\Huge\$ as $\displaystyle-{5}{x}-{2}{x}\usepackage{cmbright}\Huge\$ , but while factoring by grouping you made a mistake with signs. If you have an expression like $\displaystyle-{2}{x}+{2}\usepackage{cmbright}\Huge\$ and you factor out a negative number, the signs of all the terms will change.