Question

the sum of first 20 terms of a.p is 1280;the common difference is 20 find the 4th term​

Answer 1

Step-by-step explanation:

Common difference (d) = 20

S(20) = 1280

20/2 { 2a + (20-1)20 } = 1280

10 { 2a + 380 } = 1280

2a + 380 = 128

2a = -252

a = -126

4th term = A(4) = a + 3d = -126 + 3(20)

= -126 + 60 = -66