Question

If n-th term of an A.P. is (2n+1), whatis the sum of its first three terms ?​

Answer 1

ANSWER

IT IS GIVEN THAT N= 2N+1

N= 1

PUTTING THIS VALUE.

A(n) = 2(1)+1=3

A(2)=2(2)+1= 5

THEREFORE. D= 5-3

D=2

SO, S(3)= 3÷2{2(3)+(3-1)2}

= 3÷2{ 6+ 2×2}

=3÷2{ 6+4}

= 3÷2{10)

= 3×5

S(3) = 15

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Answer 2

Solution in attachment.

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