Answer : The required expression is,

Step-by-step explanation :
The expression with (-1) as its base that will produce a positive product is written as:

where,
'n' is a natural number
For example :
When we take the value of n = 1, then we get
which is a positive product.
When we take the value of n = 2, then we get
which is a positive product.
When we take the value of n = 3, then we get
which is a positive product.
That means when we take any natural number in this expression, then it will give a positive product.
Hence, the required expression is,
