1. **State the problem:** Convert the angle 405° from degrees to radians. 2. **Formula:** To convert degrees to radians, use the formula: $$\text{radians} = \text{degrees} \times \frac{\pi}{180}$$ 3. **Apply the formula:** $$405^\circ \times \frac{\pi}{180}$$ 4. **Simplify the fraction:** $$\frac{405}{180} = \frac{\cancel{45}9}{\cancel{45}4} = \frac{9}{4}$$ 5. **Final answer:** $$405^\circ = \frac{9\pi}{4} \text{ radians}$$ This means 405 degrees is equivalent to $\frac{9\pi}{4}$ radians.