Question

If end term of an ap is within bracket 2 n + 1 write the sum of its first 3 terms

Answer 1

1st term = 2n+1

= 2(1)+1= 2+1= 3

second term = 2(2)+1

= 4+1= 5

third term =2(3)+1= 7

sum of first three term

S3= n/2 ×2a +(n-1)×D

3/2× 2(3)+(3-1) × 2

3/2×6+2(2)

3/2× 6+4

3/2×10

3×5 = 15