Let us consider a right ∆ABC, right angled at B and ∠C = θ.
Now, it is given that cosec θ = 2.
Also, sin θ = 1/cosec θ = 1/2 = AB/AC

So, if AB =k, then AC =2k, where k is a positive number.
Using Pythagoras theorem, we have:

Finding out the other T-ratios using their definitions, we get:

Substituting these values in the given expression, we get:

i.e., LHS = RHS
Hence proved.