急 (2sina+cosa)÷(sina-3cosa)=-5 求3cos2a+4sin2a的值
1个回答
根据已知可以整理算出tana=2
tan2a=-4/3 cos2a=3/5或者-3/5 sin2a=-4/5或4/5
这样
3cos2a+4sin2a=±7/5
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