cho cos a =-4/5 vs pi/2 25/10/2021 Bởi Reese cho cos a =-4/5 vs pi/2 { "@context": "https://schema.org", "@type": "QAPage", "mainEntity": { "@type": "Question", "name": " cho cos a =-4/5 vs pi/2
$\frac{\pi}{2}<a<\pi$ $\Rightarrow sina>0, cosa<0$ $\Rightarrow sina=\sqrt{1-cos^2a}= \frac{3}{5}$ $M= 10sina+5cosa=10.\frac{3}{5}+5.\frac{-4}{5}= 2$ Bình luận
$\frac{\pi}{2}<a<\pi$
$\Rightarrow sina>0, cosa<0$
$\Rightarrow sina=\sqrt{1-cos^2a}= \frac{3}{5}$
$M= 10sina+5cosa=10.\frac{3}{5}+5.\frac{-4}{5}= 2$