Question

find sum of infinite series 1+4+13..​

Answer 1

Answer:first white the whole question

Step-by-step explanation:

Answer 2

Answer:

$\underline\huge{ANSWER}$

Step-by-step explanation:

GIVEN :

• sum of n terms of series

SOLUTION :

→ difference of the sum= 3+9+27+....................(n-1)

  ⇒if we take 1 common

     1+(3+9+27+...............(n-1))

→ $T_n=\frac{3^n-1}{3-1}$

→ $T_n=\frac{3^n-1}{2}$

→ $\frac{1}{2}$ ∑$3^n-$∑1

→ $\frac{1}{2}(3+3^2+.........+3^n-n)$

→ $\frac{3^(n-1)-n-1}{4-2}$

→ $\frac{3^n+1-2n-3}{4}$