Do $\pi/2<\alpha < \pi \Rightarrow cos\alpha <0 $. Ta có: $sin\alpha^{2}+cos\alpha^{2}=1 \Rightarrow cos\alpha= \frac{-4}{5}$.$tan\alpha=\frac{sin\alpha }{cos\alpha}=\frac{-3}{4}$.....Thay vào đề.....
Do $\pi/2<\alpha < \pi \Rightarrow cos\alpha <0 $. Ta có: $sin\alpha^{2}+cos\alpha^{2}=1 \Rightarrow cos\alpha= \frac{-4}{5}$.$tan\alpha=\frac{sin\alpha }{cos\alpha}-\frac{-3}{4}$.....Thay vào đề.....
Do $\pi/2<\alpha < \pi \Rightarrow cos\alpha <0 $. Ta có: $sin\alpha^{2}+cos\alpha^{2}=1 \Rightarrow cos\alpha= \frac{-4}{5}$.$tan\alpha=\frac{sin\alpha }{cos\alpha}
=\frac{-3}{4}$.....Thay vào đề.....