Simplify the numerical expression (-0.9)^2.

The simplified form is
  

0.81

To simplify the numerical expression (-0.9)^2, we need to multiply -0.9 by itself.

The square of any number is obtained by multiplying the number by itself. So, in this case, we need to multiply -0.9 by -0.9.

Using the rule of multiplying two negative numbers, the result will be positive.

So, (-0.9)^2 = (-0.9) x (-0.9) = 0.81.

Therefore, the simplified form of (-0.9)^2 is 0.81.

(-0.9)^2 = 0.81