1+sin2B=(sinB+cosB)^2
cos^2B-sin^2B=(cosB+sinB)(cosB-sinB)
所以1+sin2B/cos^2B-sin^2B=sinB+cosB/cosB-sinB
分子分母同时除以cosB得到1+tanB/1-tanB=-3
可得到tanB=2
所以B=kπ+arctan2
1+sin2B/cos^2B-sin^2B=-3
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