计算:tan300°•cot287°+tan240°•tan193°-cot287°•tan193°=______.
1个回答

tan300°•cot287°+tan240°•tan193°-cot287°•tan193°

=tan120°cot107°+tan193°(tan240°-cot287°)

=-tan60°(-tan17°)+tan13°(tan60°-cot107°)

=

3tan17°+tan13°(

3+tan17°)

=

3(tan17°+tan13°)+tan13°tan17°

=

3tan(13°+17°)(1-tan13°tan17°)+tan13°tan17°

=1-tan13°tan17°+tan13°tan17°=1,

故答案为:1.