Question

The sum of the 7th terms of an AP is 63 and the sum of its next 7 terms is 161 find the 28th term of this AP​

Answer 1

Answer:

A⁷=63

A¹⁴=161

Now,

A⁷= a + 6d

63 = a+ 6d

a + 6d = 63 equation 1

a¹⁴= a + 13d

161= a + 13d

a + 13d = 161 equation 2

Subtracting equation 1 and equation 2 ,we get

7d = 98

d = 98÷7

d = 14

Now putting d = 14 in equation 1

a + 6(14) = 63

a + 84 = 63

a = 63 - 84

a = –21

Now to find 28 term

a²⁸= a + (n-1)d

= –21 + (28 ‐ 1)14

–21 + 378

a²⁸ = 357