为方便表示，将原待证命题改写为： \forall x\in\mathbb R, |\!\cos x|+|\!\cos 2x|+\cdots+|\!\cos nx|\ge\frac{n-1}2\qquad(n\in\mathbb Z_{>0})\\要证明这个命题，首先考虑证明如下引理： 引理：对任意正整数 n ，都有 ...

This circle has the centre at the origin and a radius of 1 unit. The point P can move around the circumference of the circle. At point P the \(x\)-coordinate is \(\cos{\theta}\) and the \(y ...

The COS x Linda Farrow collection features reworked archival styles including aviator, rectangle, cat-eye and square frames ...

The collaboration takes classic silhouettes and makes them modern, from cat eyes to aviators and even 70s-style square shades ...