The trigonometric expression $tobe$ used for substitution $in{\displaystyle \underset{\frac{2}{5}}{\overset{\frac{4}{5}}{}}}\frac{\sqrt[\phantom{2}]{25x^2-4}}{x}dx.$

$x=\frac{2}{5}sec$

$x=\frac{2}{5}cos$

$x=\frac{2}{5}tan$

$x=\frac{2}{5}sin$