原式=sin40(sin10/cos10-tan60)
=sin40(sin10/cos10-sin60/cos60)
=sin40[(sin10cos60-sin60cos10)/cos10cos60]
=2sin40(sin-50)/cos10
=-2sin40cos40/sin80=-sin80/sin80=-1
原式=sin40(sin10/cos10-tan60)
=sin40(sin10/cos10-sin60/cos60)
=sin40[(sin10cos60-sin60cos10)/cos10cos60]
=2sin40(sin-50)/cos10
=-2sin40cos40/sin80=-sin80/sin80=-1