You may have made a mistake while simplifying. To calculate tangent, use $\displaystyle{\tan{\theta}}=\frac{{y}}{{x}}\usepackage{cmbright}\Huge\$ . Remember that dividing by a fraction is the same as multiplying by its reciprocal. The correct answer is $\displaystyle\frac{\sqrt{{3}}}{{3}}\usepackage{cmbright}\Huge\$ .