No, it is not equivalent to (x5)3. If yoh were to put 1 as a substitute for x5; 1 × 1× 1 equals 1, as represented in x5x5x5. The thing is (1)3 equals 3, as shown in (x5)3. You can substitute x5 for any number. x5x5x5 is more like it is raised to the third power than multiplied by 3.
