Question

If the sum terms of first 7 terms of an AP whose second and third terms are 14 and 18 respectively ​

Answer 1

Step-by-step explanation:

The required A.P is 10,14,18,....

Here a = 10 , d=t3-t2 = 18-14 = 4 S7= ? n=7

Therefore, Sn = n [ 2a + ( n-1) d ]

2

S7 = 7 [ 2(10) + (7-1) 4 ]

2

S7 = 7 [ 20 + 6 × 4 ]

2

S7 = 7 [ 20 + 24 ]

2

S7 = 7 [ 44 ]

2

S7 = 7 × 22

S7 = 154

Hence, the sum of first 7 terms is 154.

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