Answer
$(ab)^{x}=a^{x}.a^{y}$
This is known as fourth Law of Exponents; where $x$ and $y$ are real numbers.
Work Step by Step
We already know that $b^{x}=e^{xlnb}$
Now,
$(ab)^{x}=e^{xln(ab)}$
This implies
$(ab)^{x}=e^{x(lna+lnb)}$
Using formula, $e^{x+y}=e^{x}.e^{y}$
$(ab)^{x}=e^{x(lna+lnb)}=e^{xlna}.e^{xlnb}$
Hence,
$(ab)^{x}=a^{x}.a^{y}$
This is known as fourth Law of Exponents; where $x$ and $y$ are real numbers.