[tex]∫ \frac{1}{ \sqrt{ {9x}^{2} + 4 } } = ∫ \frac{1}{ \sqrt{9( {x}^{2} + \frac{4}{9}) } } \\ = ∫ \frac{1}{3 \sqrt{ {x}^{2} + \frac{4}{9} } } = \frac{1}{3} ∫ \frac{1}{ \sqrt{ {x}^{2} + \frac{4}{9} } } \\ = \frac{1}{3} \times ln(x + \sqrt{ {x}^{2} + \frac{4}{9} } ) + c.[/tex]
