Question

find the sum of infinite series 1-4x+7x^2+.........​

Answer 1

please give me thanks

1/5

S= 1+ 4x + 7x^2 + 10x^3...........(1)

x*S= x + 4x^2 + 7x^3 + 10x^4......(2)

subtracting (2) from (1)

S-x*S = 1+ 3x + 3x^2 + 3x^3....

S*(1-x) = 1+3*(x+x^2+x^3)...

Now x < 1

S*(1-x) = 1+ 3 *(x/(1-x))

Now S=35/16