Show that − 1 ≤ sin x ≤ 1 {\displaystyle {}-1\leq \sin x\leq 1} and − 1 ≤ cos x ≤ 1 {\displaystyle {}-1\leq \cos x\leq 1} holds for all x ∈ R {\displaystyle {}x\in \mathbb {R} } .
