cho cot a =1/2 ( pi 25/10/2021 Bởi Clara cho cot a =1/2 ( pi { "@context": "https://schema.org", "@type": "QAPage", "mainEntity": { "@type": "Question", "name": " cho cot a =1/2 ( pi
Ta có $\dfrac{1}{\sin^2a} = 1 + cot^2a$ $<-> \dfrac{1}{\sin^2a} = \dfrac{5}{4}$ $<-> \sin^2a = \dfrac{4}{5}$ $<-> \sin a = \pm\dfrac{2}{\sqrt{5}}$ Do $\pi < a < \dfrac{3\pi}{2}$ nên $\sin a < 0$. Vậy $\sin a = – \dfrac{2\sqrt{5}}{5}$ Bình luận
Ta có
$\dfrac{1}{\sin^2a} = 1 + cot^2a$
$<-> \dfrac{1}{\sin^2a} = \dfrac{5}{4}$
$<-> \sin^2a = \dfrac{4}{5}$
$<-> \sin a = \pm\dfrac{2}{\sqrt{5}}$
Do $\pi < a < \dfrac{3\pi}{2}$ nên $\sin a < 0$. Vậy
$\sin a = – \dfrac{2\sqrt{5}}{5}$