Question

find the sum of 19 term of the series:24+21+18+15+........... described this question​

Answer 1

As per the question,

a=24.

d=21-24= -3.

=>S(n)=-351.

=>n/2{2a+(n-1)d}=-351.

=>n/2{2*24+(n-1)-3=-351.

=>n/2(48-3n+3)=-351.

=>n/2(51-3n)=-351.

=>n(51-3n)=-351*2.

=>51n-3n^2=-702.

=>51n-3n^2+702=0.

=>-3(n^2-17n-234)=0.

=>n^2-17n-234=0/-3=0.

=>n^2-26n+9n-234=0.

=>n(n-26)+9(n-26)=0.

=>(n-26)((n+9)=0.

We have got two roots.

We'll discard n+9 as it gives-ve value.

So, n-26=0.

=>n=26.

So,26 terms of AP series 24+18+15+... Will have to be taken continuously so that their sum is -351.

Hope it helps.

Answer 2

Answer:

Hope this will help you