The expression with '-1' as its base that will produce a positive product is
[tex] (-1)^{2n} [/tex] , where n is a natural number.
If we take n=1, we get [tex] (-1)^{2n}=(-1)^{2 \times 1}= 1 [/tex] which is positive.
If we take n=2, we get [tex] (-1)^{2n}=(-1)^{2 \times 2}= 1 [/tex] which is also positive.
Similarly if we take any natural number in this expression, it will give a positive product.
Hence, [tex] (-1)^{2n} [/tex] is the required expression.
