(x²+x+1)+(x²-x+1)

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

Looking at the terms with x², we have x² + x² = 2x².

Looking at the terms with x, we have x - x = 0x, so the x term disappears.

Finally, the constant terms are 1 + 1 = 2.

Putting it all together, the sum is:

2x² + 2