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# Why can’t we write -a=b^x/y ?

If we are given to solve a^y=b^x then we solve it by making a=b^x/y. My question is if y is even why can’t we write -a instead of a in LHS because if we are given 4= x^2 we write x=+2 or -2? I am very confused, so please help.

### 1 Answer

- ?Lv 71 year agoFavorite Answer
x^2 = y ... y is a variable, not a constant like 4

... different rules apply

a^y = b^x

a = b^(x/y) until you know a number value for b and y (which has become a root) we don 't know if the answer is pos, neg, or imaginary.