Question

# If the nth term of an is $$(2n+1)$$,find the sum of the first n terms of the AP.

Solution

## $$a_n=2n+1$$$$a_1=2+1=3$$$$a_2=2\cdot2+1=5$$$$d=a_2-a_1$$$$=5-3=2$$$$S_n=\dfrac { n }{ 2 } [2a+(n-1)d]$$$$=\dfrac { n }{ 2 }[6+(n-1)2]$$$$=\dfrac {n }{ 2 }[2n+4]$$  Maths

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