Question

8th term of an arithmetic sequence is 56.Find the sum of first 15 terms​

Answer 1

Answer:

840

Step-by-step explanation:

8th term = 56

=> a + 7d = 56

Multiply 2 both the sides,

2a + 14d = 112 (1)

Now, Sum of first 15 terms -

= 15/2 × ( 2a + 14d )

= 15/2 × 112 [ From (1) ]

= 15 × 56 = 840

Answer 2

Answer:

840

Step-by-step explanation:

s15=840

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