If nth term of an A.P is $$(2n+1)$$, what is the sum of its first three terms?

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Text solutionVerified

$$T_n=2n+1$$

$$T_1=a=2(1)+1=3$$

$$T_2=a+d=2(2)+1=5$$

$$a+d=5\Rightarrow 3+d=5\Rightarrow d=2$$

$$a=3, d=2$$

$$S_3=\dfrac{3}{2}[2a+(3-1)d]$$

$$=\dfrac{3}{2}[2\times 3+2\times 2]$$

$$=3\times 5=15$$.

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Question Text	If nth term of an A.P is $$(2n+1)$$, what is the sum of its first three terms?
Answer Type	Text solution:1
Upvotes	150