Advertisements
Advertisements
Question
Find the sum of the sequence `-1/3, 1, -3, 9, ..........` upto 8 terms.
Advertisements
Solution
Here, `1/(-1/3) = (-3)/1`
= `9/(-3)`
= –3
Thus, the given sequence is a G.P. with first term (a) = `-1/3` and common ratio (r) = –3 ...(∵ r < 1)
Number of terms to be added, n = 8
∴ `S_n = (a(1 - r^n))/(1 - r)`
`=> S_8 = (-1/3(1 - (-3)^8))/(1 + 3)`
= `(-1 + 3^8)/12`
= `1/12 (3^8 - 1)`
RELATED QUESTIONS
Find, which of the following sequence from a G.P. :
`1/8, 1/24, 1/72, 1/216, ................`
Find the G.P. whose first term is 64 and next term is 32.
The fifth term of a G.P. is 81 and its second term is 24. Find the geometric progression.
If the first and the third terms of a G.P. are 2 and 8 respectively, find its second term.
Find the geometric progression with 4th term = 54 and 7th term = 1458.
How many terms of the geometric progression 1 + 4 + 16 + 64 + …….. must be added to get sum equal to 5461?
Q 3.1
Q 3.3
Q 7
The first two terms of a G.P. are 125 and 25 respectively. Find the 5th and the 6th terms of the G.P.
