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Question Number 201517 by sonukgindia last updated on 08/Dec/23

Answered by Calculusboy last updated on 08/Dec/23

Solution: let 𝛉=(𝛑/2)−x  d𝛉=−dx  when x=(𝛑/2)   𝛉=0  and when x=0  𝛉=(𝛑/2)  I=∫_0 ^(𝛑/2) (1/(1+((1/(tanx)))^n ))dx  ⇔  I=∫_0 ^(𝛑/2) (1/(((tanx)^n +1)/((tanx)^n )))dx    I=∫_0 ^(𝛑/2)  (((tanx)^n )/(1+(tanx)^n ))dx  I=∫_(𝛑/2) ^0  (([tan((𝛑/2)−𝛉)]^n )/(1+[tan((𝛑/2)−𝛉)]^n ))(−d𝛉)     Nb: tan((𝛑/2)−𝛉)=cot𝛉     I=∫_0 ^(𝛑/2)  (((cot𝛉)^n )/(1+(cot𝛉)^n ))d𝛉   (changing of variable)  I=∫_0 ^(𝛑/2)  (((cotx)^n )/(1+(cotx)^n ))dx    (add the two integral)  I+I=∫_0 ^(𝛑/2) (1/(1+(cotx)^n ))dx+∫_0 ^(𝛑/2) (((cotx)^n )/(1+(cotx)^n ))dx  2I=∫_0 ^(𝛑/2)  ((1+(cotx)^n )/(1+(cotx)^n ))dx  ⇔  2I=∫_0 ^(𝛑/2) 1 dx   2I=x∣_0 ^(𝛑/2)  +C  2I=((𝛑/2)−0)  I=(𝛑/4)

Solution:letθ=π2xdθ=dxwhenx=π2θ=0andwhenx=0θ=π2I=0π211+(1tanx)ndxI=0π21(tanx)n+1(tanx)ndxI=0π2(tanx)n1+(tanx)ndxI=π20[tan(π2θ)]n1+[tan(π2θ)]n(dθ)Nb:tan(π2θ)=cotθI=0π2(cotθ)n1+(cotθ)ndθ(changingofvariable)I=0π2(cotx)n1+(cotx)ndx(addthetwointegral)I+I=0π211+(cotx)ndx+0π2(cotx)n1+(cotx)ndx2I=0π21+(cotx)n1+(cotx)ndx2I=0π21dx2I=x0π2+C2I=(π20)I=π4

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