An AP 5,12,19.....has 50 terms. Find its last term. Hence find the sum of last 15 terms
Answers
Answered by
7
a=5
d=12-5=7
n=50
an=a+(n-1)d
5+(50-1)7
5+343
348
For sum of last 15 terms =
a=-5
d=-7
n=36
S36=n/2[2a+(n-1)d]
=-4230
d=12-5=7
n=50
an=a+(n-1)d
5+(50-1)7
5+343
348
For sum of last 15 terms =
a=-5
d=-7
n=36
S36=n/2[2a+(n-1)d]
=-4230
THANU85:
Hi
How n=36 came???
For sum of last. 15 terms
Answered by
4
Sum is 810 and last term i. e. a(n)=348
Attachments:
sorry
sum was from last term
Given A.P is 5,12,19.......505,12,19.......50 terms
a=5;d=7;n=50a=5;d=7;n=50
an=a+(n−1)dan=a+(n−1)d
an=5+49×7an=5+49×7
=5+343=348=5+343=348
Sn=n2Sn=n2[2n+(n−1)d][2n+(n−1)d]
Sum of the last 15 terms
a=348,d=−7,n=15a=348,d=−7,n=15
S=152S=152[2×348−(14)(−7)][2×348−(14)(−7)]
=152=152[696+98][696+98]
=15×397=15×397
=5955=5955
Hence the sum of last 15 terms =5955
a=5;d=7;n=50a=5;d=7;n=50
an=a+(n−1)dan=a+(n−1)d
an=5+49×7an=5+49×7
=5+343=348=5+343=348
Sn=n2Sn=n2[2n+(n−1)d][2n+(n−1)d]
Sum of the last 15 terms
a=348,d=−7,n=15a=348,d=−7,n=15
S=152S=152[2×348−(14)(−7)][2×348−(14)(−7)]
=152=152[696+98][696+98]
=15×397=15×397
=5955=5955
Hence the sum of last 15 terms =5955
It was right
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