An arteriole constricts to one half of its original radius. Resistance to flow changes by what factor?

1. Resistance is inversely proportional to the radius raised to the fourth power. 2. Halving the radius means the new radius is one half of the old. 3. One half raised to the fourth power is one sixteenth. 4. Resistance is the inverse of that, so it rises by a factor of 16. 5. The mirror case confirms it: doubling the radius drops resistance to one sixteenth and raises flow 16 times. 6. A factor of 4 would follow if resistance depended on radius squared, which it does not. 7. Any falling answer inverts the direction, because constricting a vessel raises resistance rather than lowering it. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 20 "The Cardiovascular System: Blood Vessels and Circulation", section 20.2 Blood Flow, Blood Pressure, and Resistance_