Concept:Use the identity cosec2θ−1=cot2θ and then integrate by substitution.Explanation:Start with the integral:∫x1−nncosec2xn−1dx.Using cosec2xn−1=cot2xn, the square root becomes ∣cotxn∣.For the standard integral, we take the positive value, so the integrand is:x1−nncotxn=nxn−1cotxn.Now substitute:t=xn⇒dt=nxn−1dx.The integral becomes:∫cottdt=log∣sint∣+C.Replace t with xn:log∣sin(xn)∣+C.This matches the form log(sinxn)+c.Answer:Option B: log(sinxn)+c.