1。已知sin（α+π/3）+sinα＝-4根號3/5（-π/2<α<0）,求cosα的值。2。已知sinxcosy=tanαcotγ,sinycosx=tanβcotγ,sin(x+y)sin(x-y)=cos平方γ。求證：sec2^α-sec2^β=sin2^γ
1。已知sin（α+π/3）+sinα＝-4根號3/5（-π/2<α<0）,求cosα的值。2。已知sinxcosy=tanαcotγ,sinycosx=tanβcotγ,sin(x+y)sin(x-y)=cos平方γ。求證：sec2^α-sec2^β=sin2^γ