1. **State the problem:** We are given the equation $\log x = 4$ and need to find the value of $x$. 2. **Recall the definition of logarithm:** The equation $\log x = 4$ means that $x$ is the number such that $10^4 = x$ because the common logarithm (log base 10) satisfies $\log_{10} x = y \iff x = 10^y$. 3. **Apply the formula:** Using the definition, we have $$x = 10^4$$ 4. **Calculate the value:** $$10^4 = 10000$$ 5. **Conclusion:** Therefore, the value of $x$ is 10000.