Question

find the sum of first n natural numbers and hence find the sum of first 20 natural numbers

please explain it and share on a photo please
step by step
class 10
chapter 3​

Answer 1

Answer:

your answer☝️

Step-by-step explanation:

solved step by step ok

and shared photo

Answer 2

To Find :

• The sum of first n natural numbers =?
• The sum of first 20 natural numbers =?

Step-by-step explanation :

As We know that, the even Natural numbers are as follows -

2, 4, 6, 8, ...

So, the nth term

★ nth terms = a + ( n - 1)d

Where,

• a = first terms
• n = Total Number of given terms
• d = common Defference

So, Now keep all values

==> nth terms = 2 + (n - 1)(2)

==> nth terms = 2 + 2n - 2

==> nth terms = 2n

So, the sum of first n even Natural numbers be,

★ Sum of nth terms = n/2 (a + l)

where,

• l = last terms

keep all required values

==> Sn = n/2 (2 + 2n)

==> Sn = n (1 + n)

==> Sn = n (n + 1) [Answer]

Now, Calculate

sum of first 20 even Natural numbers be,

==> S20 = n(n + 1)

where,

• n = 20

==> S20 = 20 (20 + 1)

==> S20 = 20 × 21

==> S20 = 420 [Answer].

Hence

• The sum of first n natural numbers = n (n + 1).
• The sum of first 20 natural numbers = 420.

_______________