Question

If the nth term of an ap is (2n+1) what is the sum of its first three terms

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

Answer:

Sum of it's first three terms is 15.

Step-by-step explanation:

Given

ax = 2x + 1

For x = 1

a1 = 2 x 1 +1 = 3 = a

For x = 2

a2 = 2 x 2 + 1 = 5

Common difference

d = a2-a1

=> 5-3

=> 2

Ax = x/2[2a+(x-1)d]

For x = 3

S3 = 3/2[2 x 3 + (3 - 1) x 2

=> 3/2[6 + 2 x 2]

=> 3/2[6 + 4]

=> 3/2 x 10

=> 15