Question

Find the sum of first 123 even natural numbers.

The first n even natural numbers are: 2, 4, 6, 8, ...., 2n

They form an A.P. with a = _____, t = _____

∴ S = _____

=

n

2

[ 2 + 2n ]

=

n

2

× 2 [ 1 + n ]

= _____

Now S = 123 × _____

= 123 × 124

∴ S = _____

Thus, the sum of first 123 even natural numbers is _____​

Answer 1

Answer:

We know that even natural numbers are 2,4,6,8,10.......

a=2

d=2

n=123

S=2n[2a+(n−1)d]

S=2123[2×2+(123−1)×2]

S=2123[4+122×2]

S=123×124

S=15252