1. **State the problem:** Simplify the expression $-2a + a^2$. 2. **Identify terms:** The expression has two terms: $-2a$ (a linear term) and $a^2$ (a quadratic term). 3. **Check for like terms:** Since $-2a$ and $a^2$ have different powers of $a$, they are not like terms and cannot be combined. 4. **Write the simplified expression:** The expression is already simplified as $a^2 - 2a$. 5. **Optional factorization:** We can factor the expression by taking $a$ common: $$a^2 - 2a = a(a - 2)$$ This is the factored form. **Final answer:** $$a^2 - 2a = a(a - 2)$$