Q. 84.5( 181 Votes )

# Find the sum of first 51 terms of an AP whose second and third terms are 14 and 18 respectively.

Answer :

**To Find: S _{51}**

**Given: a**

_{2}= 14, a_{3}= 18We have; a

_{2}= 14, a

_{3}= 18 and n = 51

We know,

d = a_{3} – a_{2} = 18 – 14 = 4

Therefore, **d = 4**

a_{2} – a = 4

14 – a = 4

a = 10

So, first term = 10Now, sum can be calculated as follows:

Where, a and d are first term and common difference respectively.

= 51 x (20 + 200)/2

= 51 x 110

= 5610

**S**

_{51}= 5610Rate this question :

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