$\displaystyle{\left({x}+{2}\right)}{\left({x}+{5}\right)}={{x}}^{{2}}+{5}{x}+{2}{x}+{10}={{x}}^{{2}}+{7}{x}+{10}\usepackage{cmbright}\Huge\$ , not $\displaystyle{{x}}^{{2}}-{7}{x}+{10}\usepackage{cmbright}\Huge\$ . You first need to find two numbers whose product is 10 and whose sum is $\displaystyle-{7}\usepackage{cmbright}\Huge\$ .