What fraction is the same even though it's upside down (not including ones)?

Suppose the fraction is x. Then the upside down fraction is 1/x (x cannot be 0 since in that case the upside down fraction is not defined).The two fractions are the same.

Therefore x = 1/x.

Multiplying both sides by x gives x^2 = 1

And that only has the solutions x = 1 and x = -1.

So, not including ones leave the fraction -1 (or in ratio form, -1/1).