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n-0-1-n-2n-1-1-pi-4-2-pi-2-12-3-pi-8-4-pi-2-6-




Question Number 53620 by kaivan.ahmadi last updated on 23/Jan/19
Σ_(n=0) ^∞    (((−1)^n )/(2n+1)) =?    1. (π/4)        2. (π^2 /(12))     3. (π/8)     4. (π^2 /6)
n=0(1)n2n+1=?1.π42.π2123.π84.π26
Commented by turbo msup by abdo last updated on 24/Jan/19
1)(π/4)  if you want method see the  platform.
1)π4ifyouwantmethodseetheplatform.
Commented by kaivan.ahmadi last updated on 24/Jan/19
thank you sir
thankyousir
Commented by turbo msup by abdo last updated on 24/Jan/19
you are welcome
youarewelcome
Commented by maxmathsup by imad last updated on 26/Jan/19
let S(x) =Σ_(n=0) ^∞   (((−1)^n )/(2n+1)) x^(2n+1)    with ∣x∣<1  due to uniform convergence we have  (d/dx)S(x) =Σ_(n=0) ^∞  (−1)^n  x^(2n)  =Σ_(n=0) ^∞  (−x^2 )^n  =(1/(1+x^2 )) ⇒  S(x) =∫_0 ^x  (dt/(1+t^2 ))  +c =arctan(x)+c   c =S(o) =0 ⇒S(x) =arctanx and Σ_(n=0) ^∞  (((−1)^n )/(2n+1)) =S(1) =arctan(1)=(π/4) .
letS(x)=n=0(1)n2n+1x2n+1withx∣<1duetouniformconvergencewehaveddxS(x)=n=0(1)nx2n=n=0(x2)n=11+x2S(x)=0xdt1+t2+c=arctan(x)+cc=S(o)=0S(x)=arctanxandn=0(1)n2n+1=S(1)=arctan(1)=π4.
Answered by tanmay.chaudhury50@gmail.com last updated on 24/Jan/19
S_n =(1/1)−(1/3)+(1/5)−(1/7)+...∞  Gregory series  tan^(−1) x=∫(dx/(1+x^2 ))  tan^(−1) x=∫(1−x^2 +x^4 −x^6 +...)dx                 =x−(x^3 /3)+(x^5 /5)−(x^7 /7)+...  put x=1 both side  tan^(−1) (1)=1−(1/3)+(1/5)−(1/7)+...  So S_n =tan^(−1) (1)=(π/4)
Sn=1113+1517+Gregoryseriestan1x=dx1+x2tan1x=(1x2+x4x6+)dx=xx33+x55x77+putx=1bothsidetan1(1)=113+1517+SoSn=tan1(1)=π4
Commented by tanmay.chaudhury50@gmail.com last updated on 24/Jan/19
Commented by tanmay.chaudhury50@gmail.com last updated on 24/Jan/19
Commented by turbo msup by abdo last updated on 24/Jan/19
thank you sir for this formulas
thankyousirforthisformulas
Commented by tanmay.chaudhury50@gmail.com last updated on 24/Jan/19
most welcome sir...i have just shared the information
mostwelcomesirihavejustsharedtheinformation
Commented by kaivan.ahmadi last updated on 24/Jan/19
thank you sir^
thankyousir
Commented by Meritguide1234 last updated on 25/Jan/19
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