Question

If a=3 and t6-27
find the sum of the
first six terms
of the A.P.​

Answer 1

Step-by-step explanation:

= 6/2(3+27). =3(30). Therefore, the sum of first six terms of an AP is 90.

Answer 2

Answer:

Let a be the first term and d be the common difference of the given A.P. Then,

S

6

=42⟹

2

6

{2a+(6−1)d}=42⟹2a+5d=14 ...(i)

It is given that

a

10

:a

30

=1:3

⟹

a+29d

a+9d

=

3

1

⟹3a+27d=a+29d

⟹2a−2d=0

⟹a=d ...(ii)

putting the value of a in (i), we get

2d+5d=14⇒d=2

∴a=d=2

∴a

13

=a+12d=2+2×12=26

Hence, first term =2 and thirteenth term =26