Question Number 115224 by mohammad17 last updated on 24/Sep/20

Answered by Dwaipayan Shikari last updated on 24/Sep/20

S=1−(1/3)+(1/9)−(1/(27))+....=(1/(1+(1/3)))=(3/4)  S_n =Σ_(n=0) ^∞ (−1)^(n+2) .(1/3^n )

Answered by Dwaipayan Shikari last updated on 24/Sep/20

f(x)=xcos3x  cos3x=1−(((3x)^2 )/2)+(((3x)^4 )/4)−....  xcos3x=x−(x^3 /2).3^2 +(x^5 /4).3^4 −...