is it any wrong in calculation of derivatives?

[grmos]

Why in equation (8) derivitiveα are devided with sin(θj) ? where does this come from?
I refer to this paper(CurricularFace: Adaptive Curriculum Learning Loss for Deep Face Recognition)
Can anyone help me understand because i find the same result but without sin(θyi) for example when(j=yi) and iwhen(j!=yi) i find an extra term sin(θj) that is multiplying with the existing result