An algebra problem by Ankit Vijay

Algebra Level 1

If the sum of the first n terms of an AP is given by S n = n 2 + 3 n { S }_{ n }={ n }^{ 2 }+3n , then the first term of the AP is :

2 3 4 1

Ankit Vijay by Ankit Vijay , 22, India

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

Aditya Deshpande
Jul 12, 2014

first term of A.Pand A.S are equal it is 4

1 Helpful 0 Interesting 0 Brilliant 0 Confused

Hello all, peace be upon you,

as given Sn = n^2 + 3n,

S(n-1) = (n-1)^2 + 3(n-1) = n^2 + n -2

Tn = Sn - S(n-1) = n^2 + 3n - n^2 -n + 2 = 2n + 2,

as for 1st term = T(1)....

T(1) = 2(1) + 2 = 2+2 = 4....

Thanks...

1 Helpful 0 Interesting 0 Brilliant 0 Confused

You can't apply this for the first term because 0th term doesn't exist.

mathh mathh - 6 years, 10 months ago

Thanks for this beautiful method of solving. :)

Krishna Ar - 6 years, 11 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...