Question

Помогите пожалуйста: 19.12

Answer 1

$19.12.\ \ sinx<cosx\\\\sinx-cosx<0\\\\sinx-sin(\dfrac{\pi }{2}-x)<0\\\\2\, sin(x-\dfrac{\pi}{4})\cdot cos\dfrac{\pi}{4}<0\\\\\sqrt2\cdot sin(x-\dfrac{\pi}{4})<0\\\\-\pi +2\pi n<x-\dfrac{\pi}{4}<2\pi n\ ,\ n\in Z\\\\-\dfrac{3\pi }{4}+2\pi n<x<\dfrac{\pi }{4}+2\pi n\ ,\ n\in Z$

Ответ: Б) .