Find the sum of the first 7 terms of the geometric series 7

Find the sum of the first 7 terms of the geometric series. 7 + 28 + 112 + ... What is the sum of the first 7 terms of the geometric series? (Simplify your answer.)

Solution

Here first term a₀=7

Common ratio,r= 28/7=4

S_a=a₀(rⁿ-1)/(r-1)   = 7(4⁷-1)/(4-1) = 7* 16383/3 = 38227