Are -1 and 1 like terms?

yes, they are like terms

Step-by-step explanation:

This is since they do not have a variable. Examples: 7x and 2x are like terms because they are both "x". 3x2 and −2x2 are like terms because they are both "x2". But 7x and 7x2 are NOT like terms (the exponents are different), they are unlike terms.

Yes they are

for ex: the reciprocal of 3/4 is 4/3. it is the opposite.

reciprocal definition:

a mathematical expression or function so related to another that their product is one; the quantity obtained by dividing the number one by a given quantity.