(x²+x+1)+(x²-x+1)

To simplify the expression (x²+x+1)+(x²-x+1), we can combine like terms.

First, let's group together the x² terms:

x² + x² = 2x²

Next, let's group together the x terms:

x + (-x) = 0

Finally, let's combine the constant terms:

1 + 1 = 2

Putting it all together, the simplified expression is:

2x² + 2