the sum of n number of AP is n^2+3n. find its 20th term.
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1
Sn=n²+3n
S20=20²+3*20
S20=400+60
S20=460
S20=20²+3*20
S20=400+60
S20=460
mysticd:
it is wrong, he asked , 20th term
you find sum of 20 terms=s20
thanks for judging
oh I'm sorry
Answered by
2
sum of n terms = Sn = n²+3n
S1 = 1²+3*1 = 4
s2= 2²+3*2 =4+6=10
s3=3²+3*3= 9+9=18
first term = a=a1 =s1 =4
a2=s2-s1=10-4=6
a3= s3-s2=18-10=8
∴in an ap a= 4 , d= common difference =a2-a1=6-4=2
n th term = an =a+(n-1)d
20 th term= a20 = a+19d
=4+19*2
=4+38
=42
S1 = 1²+3*1 = 4
s2= 2²+3*2 =4+6=10
s3=3²+3*3= 9+9=18
first term = a=a1 =s1 =4
a2=s2-s1=10-4=6
a3= s3-s2=18-10=8
∴in an ap a= 4 , d= common difference =a2-a1=6-4=2
n th term = an =a+(n-1)d
20 th term= a20 = a+19d
=4+19*2
=4+38
=42
u'r welcome
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