Question

Help. Найти cos a, sin a, ctg a. (10-11кл)

Answer 1

Ответ:

$tg\alpha =-1\ \ \to \ \ \ \alpha =-\dfrac{\pi}{4}+\pi n\ ,\ n\in Z\\\\\alpha \in \Big(\dfrac{\pi }{2}\ ;\ \pi \Big)\ \ \Rightarrow \ \ \ \alpha =\dfrac{3\pi }{4}\\\\\\cos\alpha =cos\dfrac{3\pi }{4}=-\dfrac{\sqrt2}{2}\ \ ,\ \ sin\alpha =sin\dfrac{3\pi}{4}=\dfrac{\sqrt2}{2}\ \ ,\ \ ctg\alpha =ctg\dfrac{3\pi}{4}=-1$