Môn Toán Lớp 10: Cho cosx= -4/5,pi/2 < x < pi , Tính sinx, tanx

Ta có:$\\$

cos^2x + sin^2x = 1 $\\$

<=> 16/25 + sin^2x = 1 $\\$

<=> sin^2x = 9/25 $\\$

<=> sinx = 3/5$\\$

=> tanx = {sinx}/{cosx} = $\dfrac{\dfrac{3}{5}}{-\dfrac{4}{5}}$ = -3/4 $\\$