$\displaystyle{\left({49}{x}-{1}\right)}{\left({x}+{121}\right)}={49}{{x}}^{{2}}+{5},{929}{x}-{1}{x}-{121}={49}{{x}}^{{2}}+{5},{928}{x}-{121}\usepackage{cmbright}\Huge\$ , not $\displaystyle{49}{{x}}^{{2}}-{121}\usepackage{cmbright}\Huge\$ . The given expression is a difference of squares, which can be factored using $\displaystyle{{r}}^{{2}}-{{s}}^{{2}}={\left({r}-{s}\right)}{\left({r}+{s}\right)}\usepackage{cmbright}\Huge\$ .