tan(2β)=2tanβ/(1-tan²β)=-3/4
α在第二象限,tanα=-√2/(7√2)=-1/7
tan(α+2β)=[tanα+tan(2β)]/[1-tanαtan(2β)]
=-1
先判定,α在第二象限,根据tanα=-1/7可进一步缩小范围到(5π/6,π)
β根据tanβ=-1/3可以缩小范围到(5π/6,π)
2β根据tan(2β)=-3/4可以进一步缩小范围到(5π/3,11π/6)
∴α+2β的范围可以定在(5π/2,17π/6)
在此范围内,α+2β=11π/4
=-7根号/10????