The sum of 5th and 16th terms of an arithmetic sequence is
67
a)what is the sum of 1st and 20th term of this sequence
b)if the 10th term is 32 what is 11th term
c)what is the sum of first 20 terms of this sequence
plz its very urgent
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16
Answer:
a.X1 +X20=X2+X19........=X5+X16=67
b.X10+X11=67
X11=67-32
=35
c. d=35-32=3
f+9d=32
f=32-(9×3)
=5
Xn=3n+2
Sn= n/2(5+3n+2)
= n/2(3n+7)
= ((3n^2)/2)+(7n/2)
=(1.5)^2+(3.5)n
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