The range of y = log base 1 / 2 index (2a-3)? Please write clearly the process

The range of y = log base 1 / 2 index (2a-3)? Please write clearly the process

Y = log base 1 / 2 index (2a-3) = - log base 2 (2a-3)
So, the range is negative, that is (negative infinity ~ 0)