Question

In an A.P, It the 3rd term and the 7th term are 450 and 510 respectively, then what is the sum of its first to termy?​

Answer 1

Let the first term of an AP be a and common difference be d

The third term of an AP is a + 2d, given that it is equal to 18

⇒a + 2d=18

The seventh term of an AP is a + 6d, given that it is equal to 30

⇒a +6d

=

30

By subtracting first equation from second equation, we get 4d = 12

⇒d=3

By substituting the value of d it in first equation, we get a = 12

Therefore sum of first 17 terms in AP is

17 (2 × 12 + (17-1) × 3) = ¹7 × 72 =

Answer 2

Answer:

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