问题
填空题
在斜△ABC中,
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答案
在斜△ABC中,
+c b
=8cosA,故b c
=8c2+b2 bc
,化简可得 3(b2+c2 )=4a2.c2+b2-a2 2bc
故
+tanA tanB
=tanA tanC
+sinAcosB cosAsinB
=sinAcosC cosAsinC
=sinAcosBsinC+sinBsinAcosC cosAsinBsinC sinAsin(B+C) cosAsinBsinC
=
=sin2A cosAsinBsinC
=a2
×bcb2 +c2-a2 2bc
=2a2 b2+c2- a2
=6,2a2
- a24a2 3
故答案为:6.