Here the number is negative.

So during multiplication care has to be taken of the sign.

The basic rules are:

Negative Number × Negative Number = Positive

Negative Number × Positive Number = Negative Number

Positive Number × Positive Number = Positive Number

The cube of -10 can be written as follows:

⟹ -10 × -10 × -10

⟹ 100 × -10

= -1000

Hence (-10)³ = -1000