Question

The statement “1 + 2 + 3 + · · · + n = n(n + 1) 2 ” for n = 3 becomes​

Answer 1

Answer:

consider 1 + 2 + 3 + … + n as an AP series with

a=1 , d=1 ,an=n

now sum of n terms of AP is

n(a+an)/2

= n(1+n)/2

hence proved.

Answer 2

Answer:

6

Step-by-step explanation:

Given that,

1 + 2 + 3 +. . . + n = n(n + 1) / 2 which is an Arithmetic progression.

Now,

AP = n( n + 1 )/2.

for n = 3,

AP = 3(3+1)/2.

= 3(4)/2.

= 12/2.

= 6.

Hence the value for n = 3 is 6.