Question Number 124963 by 676597498 last updated on 07/Dec/20

Commented by MJS_new last updated on 07/Dec/20

Answered by Dwaipayan Shikari last updated on 07/Dec/20

Commented by 676597498 last updated on 07/Dec/20

Commented by Dwaipayan Shikari last updated on 07/Dec/20

Commented by 676597498 last updated on 07/Dec/20

Commented by mr W last updated on 07/Dec/20

Commented by MJS_new last updated on 07/Dec/20

Answered by mathmax by abdo last updated on 07/Dec/20
![A =∫_0 ^(π/4) ((sinx)/(cosx +sinx))dx we do the changement tan((x/2))=t ⇒ A =∫_0 ^((√2)−1) (((2t)/(1+t^2 ))/(((1−t^2 )/(1+t^2 ))+((2t)/(1+t^2 ))))((2dt)/(1+t^2 )) =∫_0 ^((√2)−1) ((4t)/((t^2 +1)(−t^2 +2t+1)))dt =−4 ∫_0 ^((√2)−1) ((tdt)/((t^2 +1)(t^2 −2t−1))) let decompose F(t)=(t/((t^2 +1)(t^2 −2t−1))) t^2 −2t−1→Δ^′ =1+1=2 ⇒t_1 =1+(√2) and t_2 =1−(√2) ⇒ F(t)=(t/((t−t_1 )(t−t_2 )(t^2 +1))) =(a/(t−t_1 )) +(b/(t−t_2 )) +((mt +n)/(t^2 +1)) a=(t_1 /(2(√2)(t_1 ^2 +1))) =((1+(√2))/(2(√2)(3+2(√2)+1)))=((1+(√2))/(2(√2)(4+2(√2))))=((1+(√2))/(8(√2)+8))=(1/8) b =(t_2 /(−2(√2)(t_2 ^2 +1))) =((1−(√2))/(−2(√2)(3−2(√2)+1)))=((1−(√2))/(−2(√2)(4−2(√2)))) =((1−(√2))/(−8(√2)+8)) =(1/8) lim_(t→+∞) tF(t)=0=a+b+m ⇒m=−(1/4) F(o)=0 =−(a/t_1 )−(b/t_2 ) +n ⇒n=(a/t_1 )+(b/t_2 ) =(1/(8(1+(√2))))+(1/(8(1−(√2)))) =(1/8)((2/((−1))))=−(1/4) ⇒ F(t)=(1/(8(t−(1+(√2))))+(1/(8(t−(1−(√2)))))−(1/4)×((t+1)/(t^2 +1)) ⇒ ∫_0 ^((√2)−1) F(t)dt =(1/8)∫_0 ^((√2)−1) (dt/(t−1−(√2))) +(1/8)∫_0 ^((√2)−1) (dt/(t−1+(√2))) −(1/8)∫_0 ^((√2)−1) ((2t)/(t^2 +1))−(1/4)∫_0 ^((√2)−1) (dt/(t^2 +1)) =(1/8)[ln∣(t−1)^2 −2∣]_0 ^((√2)−1) −(1/8)[ln(t^2 +1)]_0 ^((√2)−1) −(1/4)[arctant]_0 ^((√2)−1) =(1/8){ln∣((√2)−2)^2 −2∣−(1/8)ln(((√2)−1)^2 +1)−(1/4)×(π/8) =(1/8)ln∣2−4(√2)+4−2∣−(1/8)ln(3−2(√2)+1)−(π/(32)) =(1/8)ln(4(√2)−4)−(1/8)ln(4−2(√2))−(π/(32)) ⇒ I=−(1/2)ln(4(√2)−4)+(1/2)ln(4−2(√2))+(π/8)](https://www.tinkutara.com/question/Q124966.png)
Commented by talminator2856791 last updated on 07/Dec/20
