已知tan(a/2)=2/5,则(2sin a+3cos a)/(3cos a-4 sin a)=

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已知tan(a/2)=2/5,则(2sin a+3cos a)/(3cos a-4 sin a)=
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已知tan(a/2)=2/5,则(2sin a+3cos a)/(3cos a-4 sin a)=
已知tan(a/2)=2/5,则(2sin a+3cos a)/(3cos a-4 sin a)=

已知tan(a/2)=2/5,则(2sin a+3cos a)/(3cos a-4 sin a)=
tana=[2tan(a/2)]/[1-tan(a/2)^2]
=20/21
(2sin a+3cos a)/(3cos a-4 sin a)
分子分母全除以cosa,则:
(2sin a+3cos a)/(3cos a-4 sin a)=(2tana+3)/(3-4tana)
=(2*20/21+3)/(3-4*20/21)
=-103/17