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Question Number 47018 by maxmathsup by imad last updated on 03/Nov/18

find ∫ (√(x+2−(√(x−1))))dx

findx+2x1dx

Commented by maxmathsup by imad last updated on 04/Nov/18

let A = ∫(√(x+2−(√(x−1))))dx  changement (√(x−1))=t give  A =∫ (√(1+t^2 +2−t))(2t)dt =2 ∫  t(√(t^2 −t+3))dt but   t^2 −t +3 =(t−(1/2))^2  +3−(1/4) =(t−(1/2))^2  +((11)/4) ⇒A=_(t−(1/2)=((√(11))/2)u)  ∫((1/2)+((√(11))/2)u)((√(11))/2)(√(1+u^2 ))((√(11))/2)du  =((11)/4) ∫ (1+(√(11))u)(√(1+u^2 ))du ⇒(4/(11)) A =_(u =shα)  ∫  (1+(√(11))shα)chαchα dα  =∫ ch^2 α dα +(√(11))∫ shα ch^2 α dα  =∫  ((1+ch(2α))/2)dα +((√(11))/3) ch^3 α +C =(α/2) +(1/4)sh(α) +((√(11))/3)ch^3 α +C  =((argsh(u))/2) +(u/4) + ((√(11))/3) ch^3 (argsh(u)) +C  =(1/2)ln(u+(√(1+u^2 ))) +(u/4) +((√(11))/3) ch^3 (ln(u+(√(1+u^2 ))) +C  =(1/2)ln(((2t−1)/(√(11))) +(√(1+(((2t−1)/(√(11))))^2 ))) +((2t−1)/(4(√(11)))) +((√(11))/3)ch^3 (ln(((2t−1)/(√(11))) +(√(1+(((2t−1)/(√(11))))))) +C  with t =(√(x−1)).

letA=x+2x1dxchangementx1=tgiveA=1+t2+2t(2t)dt=2tt2t+3dtbutt2t+3=(t12)2+314=(t12)2+114A=t12=112u(12+112u)1121+u2112du=114(1+11u)1+u2du411A=u=shα(1+11shα)chαchαdα=ch2αdα+11shαch2αdα=1+ch(2α)2dα+113ch3α+C=α2+14sh(α)+113ch3α+C=argsh(u)2+u4+113ch3(argsh(u))+C=12ln(u+1+u2)+u4+113ch3(ln(u+1+u2)+C=12ln(2t111+1+(2t111)2)+2t1411+113ch3(ln(2t111+1+(2t111))+Cwitht=x1.

Answered by tanmay.chaudhury50@gmail.com last updated on 04/Nov/18

x−1=t^2   dx=2tdt  ∫(√(t^2 +1+2−t))  ×2tdt  ∫(2t−1+1)(√(t^2 −t+3))  dt  ∫(√(t^2 −t+3))  d(t^2 −t+1)+∫(√(t^2 −2×t×(1/2)+(1/4)+3−(1/4) )) dt  I_1 +I_2   I_1 =(((t^2 −t+1)^(3/2) )/(3/2))+c_1   I_1 =(((x−(√(x−1)) )^(3/2) )/(3/2))+c_1   I_2 =∫(√((t−(1/2))^2 +(((√(11))/2))^2 )) dt  =(((t−(1/2)))/2)×(√((t−(1/2))^2 +(((√(11))/2))^2 )) +(((((√(11))/2))^2 )/2)ln{(t−(1/2))+(√((t−(1/2))^2 +(((√(11))/2))^2 ))  +c_2   =((((√(x−1)) −(1/2)))/2)×(√(((√(x−1))  −(1/2))^2 +((((√(11)) )/2))^2 )) +(((((√(11))/2))^2 )/2)ln{((√(x−1)) −(1/2))+(√(((√(x−1)) −(1/2))^2 +(((√(11))/2))^2 )) +c_2

x1=t2dx=2tdtt2+1+2t×2tdt(2t1+1)t2t+3dtt2t+3d(t2t+1)+t22×t×12+14+314dtI1+I2I1=(t2t+1)3232+c1I1=(xx1)3232+c1I2=(t12)2+(112)2dt=(t12)2×(t12)2+(112)2+(112)22ln{(t12)+(t12)2+(112)2+c2=(x112)2×(x112)2+(112)2+(112)22ln{(x112)+(x112)2+(112)2+c2

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