tan²a-sin²a-tan²asin²a=?

答：
1）
tan²a-sin²a-tan²asin²a
=tan²a(1-sin²a)-sin²a
=tan²acos²a-sin²a
=sin²a-sin²a
=0
2)
tana=-1/2
5cos²a+3sinacosa-2sin²a
=(5+3tana-2tan²a)cos²a
=(5-3/2-2/4)cos²a
=3/(1/cos²a)
=3/[(sin²a+cos²a)/cos²a]
=3/(tan²a+1)
=3/(1/4+1)
=12/5

1) ,
tan²a-sin²a-tan²asin²a
=tan²a(1-sin²a)-sin²a
=tan²acos²a- sin²a
=sin²a-sin²a
=0
2),
tana=-1/2, sina=-1/√5, cosa=2/√5
5cos²a+3sinacosa-2sin²a=5*(2/√5)^2-3*/√5)*(2/√5)-2*(1/√5)^2=4-6/5-2/5=12/5

解1 tan²a-sin²a-tan²asin²a
=tan²a-tan²asin²a-sin²a
=tan²a（1-sin²a）-sin²a
=tan²a（cos²a）-sin²a
=[sin²a/cos²...