Question

find the sum of first 21 terms of AP. whose 2nd term is 8 and 4th term is 14 ​

Answer 1

Answer:

735

Step-by-step explanation:

Given:

a + d = 8

a + 3d = 14

To find:

Solution:

a + d = 8 …....(1)

a + 3d = 14..…(2)

Subtracting eq(2) and (1), we get,  

2d = 6

d = 3

substitute in eq(1)

a + 3 = 8

a = 5

Hence the 21st term is

Hence the last term in the series (l) is  = 65

The sum of first 21 terms is 735.

Answer 2

Answer:

Here sum of first 21 terms is 735

Step-by-step explanation:

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