Answer
Option C is correct.
Step 6 contains the error.
Explanation
Looking through the steps, we can see easily that the mistake occurs at the 6th step, specifically when the process moves from step 5 to step 6
-1 + cos θ = -2 sin² (θ/2)
If one multiplies through by -1
1 - cos θ = 2 sin² (θ/2)
NOT 1 + cos θ = 2 sin² (θ/2)
Hope this Helps!!!
