已知sin(π/3 -α)=1/5求sin(2π/3 +α)和cos（7π/6 +α）的值

题目

已知sin(π/3 -α)=1/5求sin(2π/3 +α)和cos（7π/6 +α）的值
2.已知sinβ=3/5,sin(α-β）=1,求cosα的值

答案