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

Even natural numbers:-
2, 4, 6, 8, 10 ...........

This forms an AP

a = 2
n = 123
d = 2

Formula = n/2 [2a + (n-1)d]

123/2 [2(2) + (123 - 1)2]
62.5 [4 + (122)2]
62.5 [4 + 244]
62.5 * 248
15500

Hope it helps
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