已知2sina+cosa=0,则(1+2sinacosa)/(sin2a-cos2a)的值是
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已知2sina+cosa=0,则(1+2sinacosa)/(sin2a-cos2a)的值是
已知2sina+cosa=0,则(1+2sinacosa)/(sin2a-cos2a)的值是
已知2sina+cosa=0,则(1+2sinacosa)/(sin2a-cos2a)的值是
2sina+cosa=0 两边同时除以cosa 得 2tana+1=0 tana =-1/2
所以 sin2a =2tana/(1+tan²a)=-4/5
cos2a=(1-tan²a)/(1-tan²a)=3/5
所以 (1+2sinacosa)/(sin2a-cos2a)=(1+sin2a)/(sin2a-cos2a)=(1-4/5)/(-4/5-3/5)=-1/7