Question

How many terms of the sequence 1,3,9,27,... Must be taken for the sum to exceed 1000? Plz show me the working and the formulas u used.

Answer 1

Sum of cubes of natural numbers = [ n(n+1) / 2 ]^2

Answer 2

Sorry..its G.P with C.D 3

Answer 3

Sum = a(r^n -1) / (r-1)
a : first term
r : common ratio
n : number of terms

Answer 4

Put sum = 100, a=1 and r=3..find n

Answer 5

\[Sn = \frac{ a(r^n-1) }{ r-1 } >1000\]

Answer 6

Nw just Do Some manipulation and solve....