Question

solve the following ...
1) Find the sum of 4+12+20+- - - - - - - - - - + 100​

Answer 1

Answer:

=........................

Answer 2

Answer:

The answer is 676

Step-by-step explanation:

4,12,20,........,100

a=4 ,a2=12 , a3=20 ,........... n'th term= 100

d = a2-a1 = 12-4 =8

we know that ,

t n = a1 +(n-1)d

100=4+(n-1)×8

100=4+8n-8

100=8n-4

8n =100+4

8n=104

n= 104÷8

n =13 ------------(1)

sum all terms,

Sn =n÷2[2a+(n-1)d]

S13=13÷2[2×4+(13-1)×8] -------(from(1) )

S13=13÷2[8+12×8]

S13=13÷2×104

S13=13×52

S13= 676