[tex]\int\limits_{\frac{3}{4}}^{\frac{4}{3}}\frac{dx}{x\sqrt{x^2 + 1} [/tex]
[tex]\int\limits_{\frac{3}{4}}^{\frac{4}{3}}\frac{dx}{x\sqrt{x^2 + 1}}=\int\limits_{\frac{3}{4}}^{\frac{4}{3}}\frac{xdx}{x^2\sqrt{x^2 + 1}}[/tex]
Đặt [tex]t= \sqrt{x^2+1} => x^2=t^2-1 => xdx=tdt [/tex]