(x²+x+1)+(x²-x+1)

To add the two expressions (x² + x + 1) and (x² - x + 1), we can simply combine like terms.

First, let's add the x² terms: x² + x² = 2x²

Next, let's add the x terms: x + (-x) = 0

Finally, let's add the constant terms: 1 + 1 = 2

Putting it all together, the sum of (x² + x + 1) and (x² - x + 1) is: 2x² + 2