1. **Problem statement:** Solve the inequality $f(x) < 0$ using the graph of $y = f(x)$. Write the solution set in interval notation. 2. **Understanding the problem:** We need to find all $x$-values where the graph of $f(x)$ lies below the $x$-axis (i.e., where $f(x)$ is negative). 3. **Analyzing the graph:** - The graph crosses the $x$-axis near $x = -1$ going from positive to negative. - It remains below the $x$-axis until it crosses again near $x = 4$ going from negative to positive. 4. **Solution intervals:** - Since $f(x) < 0$ between these two $x$-values, the solution set is the open interval between the roots. 5. **Final answer:** $$ \boxed{(-1,4)} $$ This means $f(x)$ is negative for all $x$ strictly between $-1$ and $4$.