Question

The nth term of an A.P is (7-3n). Find the A.P and also find the sum of first 25 terms​

Answer 1

Tn = 7 - 3n

=> a + (n-1)d = 4 + 3 - 3n

=> a + (n - 1)d = 4 - 3( n - 1)

On Comparing both sides, we get

a = 4

d = - 3

Now,

Sn = 25/2 [ 2a +(25 - 1) d]

= 25/2 [ 2×4 + (24) (-3)]

= 25/2 [ 8 - 72]

= 25/2 [ -64]

= 25 × (-32)

= - 800