1 answer
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First make the substitution
p=2x,
dp=2dx
dx=(1/2)dp
I=∫cot 2x dx
=∫cot(p)(1/2)dp
=(1/2)∫(cos(p)/sin(p))dp
=(1/2)∫d(sin(p))/sin(p)
=(1/2)ln sin(p) + C
Can you take it from here?