## Functions Modeling Change: A Preparation for Calculus, 5th Edition

$$x=0,\:x=-\frac{2\sqrt{35}}{7},\:x=\frac{2\sqrt{35}}{7}$$
Solving the equation for $x$, we find: $$7x^4-20x^2=0 \\ x^2\left(\sqrt{7}x+2\sqrt{5}\right)\left(\sqrt{7}x-2\sqrt{5}\right)=0 \\ x=0,\:x=-\frac{2\sqrt{35}}{7},\:x=\frac{2\sqrt{35}}{7}$$