The sum of infinite terms of the following series $1+\dfrac {4}{5}+\dfrac {7}{{5}^{2}}+\dfrac {10}{{5}^{3}}+..$ will be
Reveal answer
Fill a bubble to check yourself
The sum of infinite terms of the following series $1+\dfrac {4}{5}+\dfrac {7}{{5}^{2}}+\dfrac {10}{{5}^{3}}+..$ will be
S = 1 + 4/5 + 7/5^2 + 10/5^3 + ... This is an arithmetico-geometric series. S = 1 + 4/5 + 7/25 + 10/125 + ... S/5 = 1/5 + 4/25 + 7/125 + ... Subtracting: 4S/5 = 1 + 3/5 + 3/25 + 3/125 + ... 4S/5 = 1 + (3/5) / (1 - 1/5) = 1 + (3/5) / (4/5) = 1 + 3/4 = 7/4. S = (7/4) * (5/4) = 35/16.
This is an arithmetico-geometric series where the sum is given by S = a/(1 - r) + dr/(1 - r)^2, with first term a = 1, common difference d = 3, and common ratio r = 1/5. Substituting these values gives S = 1/(4/5) + 3(1/5)/(4/5)^2, which simplifies to 5/4 + 15/16. Adding these fractions yields 35/16.