Q. 253.9( 22 Votes )

# Find the sum of the following series up to n terms:

Answer :

The n^{th} term of series is

Now, first solve the numerator & denominator separately

1^{3} + 2^{3} + 3^{3} + … + n^{3} …(1)

Also,

1 + 3 + 5 + … + n terms

This is an AP.

whose first term(a) =1 & common difference(d) = 3 - 1 = 2

Now, sum of n terms of AP is

S_{n} = (n/2)[2a + (n - 1)d]

= (n/2)[2(1) + (n - 1)2]

= (n/2)[2 + 2n - 2]

= (n/2)[2n]

= n^{2}

∴ S_{n} = n^{2} …(2)

Now,

putting values from (1) & (2)

Now, Finding Sum of n terms of Series

Thus, the required sum is

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