\(=\cos\left(\Pi+\dfrac{\Pi}{2}-a\right)-\sin\left(\Pi+\dfrac{\Pi}{2}-a\right)+\sin a\)
\(=-\cos\left(\dfrac{\Pi}{2}-a\right)+\sin\left(\dfrac{\Pi}{2}-a\right)+\sin a\)
\(=-\sin a+\cos a+\sin a=\cos a\)
Chứng minh đẳng thức: \(\dfrac{tan\left(\alpha-\dfrac{\pi}{2}\right).cos\left(\dfrac{3\pi}{2}+\alpha\right)-sin^3\left(\dfrac{7\pi}{2}-\alpha\right)}{cos\left(\alpha-\dfrac{\pi}{2}\right).tan\left(\dfrac{3\pi}{2}+\alpha\right)}=sin^2\alpha\)
cho \(\cos\alpha=\dfrac{-12}{13}\) biết \(\pi< \alpha< \dfrac{3\pi}{2}\)
tính \(\sin\alpha,cos2\alpha,tan\left(\alpha-\dfrac{\pi}{3}\right),sin\left(2\alpha+\dfrac{\pi}{6}\right)\)
cho cot α=\(\dfrac{1}{2}\)(π<α<\(\dfrac{3\pi}{2}\)) thì sin2α.cosα có giá trị bằng?
cho sin α = 0,6 ; π < α < \(\frac{3\pi}{2}\). tìm cosα , tanα , cotα
cho sin\(\alpha=\frac{3}{4}\) , \(\frac{\pi}{2}< \alpha< \pi\)
tinh A= \(\frac{2tan\alpha-3cot\alpha}{cos\alpha-tan\alpha}\)
cho \(sin\alpha+cos\alpha=\frac{1}{2}\) với \(\frac{3\pi}{4}< \alpha< \pi\). tính \(tan2\alpha\)
1/ \(\alpha\ne\frac{\pi}{2}+k\pi,k\in Z\) chứng minh rằng: \(\frac{\sin^2\alpha-\cos^2\alpha}{1+2\sin\cos}=\frac{\tan-1}{\tan+1}\)
Cho sin\(\alpha\)=3/4 π/2<\(\alpha\)<π tính A= 2tan\(\alpha\)-3cot\(\alpha\)/cos\(\alpha\)-tan\(\alpha\)
Tính cos(\(\alpha+\frac{\pi}{3}\)) biết sin\(\alpha=\sqrt{\frac{1}{3}}\)và \(0< \alpha< \frac{\pi}{2}\).
