Maths class 10 if nterm of an ap is 2n+1 what is the sum of its first three terms
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if an = 2n+1
then
a1=2×1+1=3
a2=2×2+1=5
a2=7
therefore,
d=a2-a1=5-3=2
now,
s=n/2(2a+(n-1)d)
s=3/2(6+4)
s=5×3
s=15
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