13)Rewrite 3^-4times 3^-5 using a single exponent.

To rewrite $$3^{-4}\times 3^{-5}$$ using a single exponent, we can use the rule of exponents that states when multiplying two numbers with the same base, we add the exponents.

So, we have:

$$3^{-4}\times 3^{-5} = 3^{-4 + (-5)}$$

Now, we can simplify the exponent by adding -4 and -5:

$$3^{-4 + (-5)} = 3^{-9}$$

Therefore, the expression $$3^{-4}\times 3^{-5}$$ can be rewritten as $$3^{-9}$$ .