1. Stating the problem: Simplify the expression $x^5 \times x^4$. 2. Formula used: When multiplying powers with the same base, add the exponents: $$a^m \times a^n = a^{m+n}$$ 3. Applying the rule: $$x^5 \times x^4 = x^{5+4}$$ 4. Simplify the exponent: $$x^{9}$$ 5. Final answer: The simplified form of $x^5 \times x^4$ is $x^9$.