#### Answer

$(x-\dfrac{9}{10})^2$

#### Work Step by Step

Given: $x^2-\dfrac{9}{5}x$
We need to add $(\dfrac{-9}{10})^2$ to complete the square.
Thus,
$x^2-\dfrac{9}{5}x+(\dfrac{-9}{10})^2=x^2-\dfrac{9}{5}x+\dfrac{81}{100}$
Apply difference of polynomial formula.
or, $x^2-2(x)(\dfrac{9}{10})+(\dfrac{9}{10})^2=(x-\dfrac{9}{10})^2$