(cos(b+15)-cosb*cos15) / (sin b * cos 15)

(cos(B+15) - cosB*cos15) / (sin B * cos 15) = 

(cosB*cos15 - sinB*sin15 - cosB*cos15) / (sin B * cos 15) = 

- sinB*sin15  / (sin B * cos 15) = -sin15  / cos 15 = -tg15 = V3 - 2

(cosBcos15 - sinBsin15 - cosBcos15) / (sinBsin15)

(-sinBsin15) / (sinBsin15) = -1