f(x) = ax
f’(x) = ax log a
\(\because\) f(x) is decreasing on R.
\(\therefore\) f’(x) < 0, ∀ x ∈ R
\(\because\) ax log a < 0, ∀ x ∈ R
\(\because\) Logarithmic function is not defined for negative values of a.
\(\therefore\) ax > 0
\(\therefore\) ax log a < 0 can be possible when log a < 0,∀ x ∈ R.
\(\therefore\) 1 > a > 0
Hence the function f(x), whose values are 1 > a > 0.
