=(sin10/cos10-sin60/cos60)*sin40
=sin40*(sin10cos60-sin60cos10)/(cos10cos60)
=-sin40sin50/(cos10cos60)
=-sin40cos40/(cos10cos60)
=-1/2*sin80/(sin80cos60)
=-1/2/(1/2)
=-1
=(sin10/cos10-sin60/cos60)*sin40
=sin40*(sin10cos60-sin60cos10)/(cos10cos60)
=-sin40sin50/(cos10cos60)
=-sin40cos40/(cos10cos60)
=-1/2*sin80/(sin80cos60)
=-1/2/(1/2)
=-1