### Instruction: Evaluate the expression $a^2\cdot a^5$ if $a= 3$.### Response: To evaluate the expression, I need to apply the rules of exponents and arithmetic.
First, I can simplify $a^2\cdot a^5$ by using the rule that $a^m\cdot a^n = a^{m+n}$.
So, $a^2\cdot a^5 = a^{2+5} = a^7$.
Now, I just need to plug in $a = 3$ and raise it to the seventh power.
I can use a calculator or do it by hand by multiplying 3 by itself seven times.
Either way, I get $3^7 = 2187$.