(1-а) •(1+а +а2) +a3

To simplify the expression, we can first distribute the multiplication:

(1 - a) • (1 + a + a^2) + a^3

Expanding the multiplication:

= 1•1 + 1•a + 1•a^2 - a•1 - a•a - a•a^2 + a^3

= 1 + a + a^2 - a - a^2 - a^3 + a^3

Combining like terms, we get:

= 1 - a

Therefore, the simplified expression is 1 - a.