tan²a-sin²a-tan²asin²a=?
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tan²a-sin²a-tan²asin²a=?
tan²a-sin²a-tan²asin²a=?
若tana=-1/2,则5cos²a+3sinacosa-2sin²a=?
tan²a-sin²a-tan²asin²a=?
若tana=-1/2,则5cos²a+3sinacosa-2sin²a=?
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
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
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