Question

find s25 of an ap whose an = 7-3n​ pls answer fast urjent

Answer 1

Given:

an = 7 - 3n

Calculating d:

an+1 - an = d
a2 = a1 = d

7-3(2) -[7-3(1)] = d

7-6 - [7-3] = d

1 - 4 = d

d = -3

D = -3, a2 = 1

a2 = a + d

1 = a -3

a = 4

Now, as we know the values of a and d we can find Sn

For S25,

(n/2)(2a + (n-1)d)

(25/2) (2(4) + (25-1)-3)

25/2 (8 + 72)

25/2 (80)

25*40

1000

So S25 of the AP will be 1000.