Dear nishat
In Triangle ACD
use sine rule
a/2 sinB /sin(180-A-B) = a/2 /sin(A-90)
sinB/sin(A+B) = -1/cosA
sinB cosA = -sin(A+B)
sinBcosA =-[sinAcosB + cosA sinB]
tanA +2tanB =0
post seperate question in different post
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