Question

If a=4 d = 1/2 find s25
​

Answer 1

If n=1 then

a1 = 7-3×1

= 4

if n=3 then

a2= 7-3×2

= 1

As a1 = 4 & a2 = 1

then d will be

=a2-a1

= -3

d= -3

S25 = 25/2(2×4 + (25-1)×-3)

=25/2 × -64

= 25× -32

= -800

Hence sum of 25 terms of this A.P will be (-800).

Step-by-step explanation:

Hope it helps

Please mark me as the brainliest

Answer 2

Answer:

Step-by-step explanation:

Assuming this is an arithmetic series

First term , a =4

Common difference , d = 1/2

Find sum of first 25 terms.

25th term = a + (25-1)d = 4 +(24)(1/2) = 4 + 12 = 16.

Sum of n terms of an AP = n/2(first term + nth term)

Sum of 25 terms = (25/2)(4+16) = 25*10 = 250