#### Answer

$2x^3-x^6$

#### Work Step by Step

Starting with the given expression: $x^3+x^3-x^3\cdot x^3$.
Multiply the last two terms, we have:
$x^3+x^3-x^6$
Combine the like terms, we have:
$2x^3-x^6$.
Since this term can no longer be simplified, therefore this is our answer.