- #1

lfdahl

Gold Member

MHB

- 749

- 0

\[\left | \cos x \right |+ \left | \cos 2x \right |+\left | \cos 2^2x \right |+...+ \left | \cos 2^nx \right |\geq \frac{n}{2\sqrt{2}}\]

- for any real x and any natural number, n.