Question

nth term of an arithmetic sequence is 4n+2. Find sum of first 25 terms of the sequence​

Answer 1

Answer:

the sum of first 25 terms of an AP whose nth term is 1 -4n is -1275.

Step-by-step explanation:

Here it is given that, an = 1 - 4n

putting, n =1 , a1 = 1- 4(1) = -3

putting, n =2 , a2 = 1 - 4(2) = -7

Therefore, a = -3 and d = (-4)

so, S25 = 25/2 [ 2(-3) + 24 (-4)]

= 25/2 [-102]

= 25 (-51 )

= -1275 Ans

hence, the sum of first 25 terms of an AP whose nth term is 1 -4n is -1275.

Answer 2

Step-by-step explanation:

An=4n+2

A1=4(1)+2 and hence,A=6

A2=4(2)+2=10

d=A2-A1=

10-6=4

n=25

Sn=n/2{2a+(n-1)d}

S²⁵=25/2{2(6)+(25-1)4}

=25/2{12+96}

25/2(100)

Answer=1250