Question

if the nth term of an A.P is (2n +1) then the sum of its first three terms is??

Answer 1

If nth term of an A.P = 2n+1

then, first term of A.P = 2(1)+1
= 2+1
= 3

then, second term = 2 (2) + 1

》4+1

》5


third term = 2 (3) +1

》6+1

》7

sum of terms = 3+5+7

sum of terms = 15

Answer 2

If the nth term of an A.P is (2n + 1) then the sum of its first three terms is 15

Given :

The nth term of an A.P is (2n + 1)

To find :

The sum of its first three terms

Solution :

Step 1 of 2 :

Find first three terms of the AP

The nth term = aₙ = 2n + 1

First term = a₁ = ( 2 × 1 ) + 1 = 2 + 1 = 3

Second Term = a₂ = ( 2 × 2 ) + 1 = 4 + 1 = 5

Third term = a₃ = ( 2 × 3 ) + 1 = 6 + 1 = 7

Step 2 of 2 :

Find sum of the first three terms

The sum of the first three terms

= 3 + 5 + 7

= 15

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