CBSE Class 10 Answered
If first term is 1 , then find the sum of first 30 terms.
Asked by sunil_0010 | 01 Jul, 2009, 10:19: PM
Expert Answer
the sum of first 20 terms of an A.P.
with first term as a and common diff as d is
20/2[2a+19d]=20a+190d..(i0
and
sum of the next 20 terms
=sum of the first 40 terms -sum of the first 20 terms
=40/2[2a+39d]- 20/2[2a+19d]
=20a+590d(ii)
acc to qn
20+190d=1/3[20a+590d]
solving we get
d=2a
is it given that first term is1?
then d=2
then you can find the sum of the first thirty terms using formula for sum of n terms.
Answered by | 01 Jul, 2009, 10:47: PM
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