Incorrect. Starting with $\displaystyle\pi{{r}}^{{2}}={50}\usepackage{cmbright}\Huge\$ , simplify the equation into the form $\displaystyle{{r}}^{{2}}=\usepackage{cmbright}\Huge\$ something before solving for r. Remember that $\displaystyle\sqrt{{{{r}}^{{2}}}}={r}\usepackage{cmbright}\Huge\$ since r is positive.