Question

已知α是第三象限角，且f（α）= sin(α- π 2 ) cos( 3π 2 +α)tan(π-α) t

已知α是第三象限角，且f（α）= sin(α- π 2 ) cos( 3π 2 +α)tan(π-α) tan(-α-π)?sin(-π-α) ．

Answer 1

f（α）= sin(α- π 2 )cos( 3π 2 +α)tan(π-α) tan(-α-π)?sin(-π-α) = sinαcosαtanα -tanα?sinα =-cosα