Question

数学解答题？

设tan（2兀一a）=-2（1）求2sina-cosa/sina+cosa的值（2）求
sin²+sinacosa-2cos²a的值

Answer 1

tan（2π-a）=tan(-a)=-tan(a)
所以tan(a)=2
(1)2sina-cosa/sina+cosa
=(2tana-1)/(tana+1)
=3/2
(2)sin²+sinacosa-2cos²a
=cos²a·(tan²a+tana-2)
=(tan²a+tana-2)/sec²a
=(tan²a+tana-2)/(1+tan²a)
=4/5