Question

find the sum of first 35 terms of an AP 11, 5, -1​

Answer 1

Step-by-step explanation:

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Answer 2

Answer:

2310

Step-by-step explanation:

a 2

=2 and a 7

=22 and n=35

We know that,

a 2

=a+d=2...(i)

and a 7

=a+6d=22...(ii)

Solving the linear equation (i) and (ii), we get

a+d−a−6d=2−22

⇒−5d=−20

⇒d=4

Putting the value of d in equation. (i), we get

a+4=2

⇒a=2−4=−2

Now, we have to find the sum of first 35 terms.

S n

= 2n

[2a+(n−1)d]

⇒S 35

= 235

[2×(−2)+(35−1)4]

⇒S 35

= 2

35 [−4+34×4]

⇒S 35

=35[−2+34×2]

⇒S 35

=35[66]

⇒S 35=2310