Question

find the sum of first 18 even number​

Answer 1

Answer:

The sum of even numbers from 2 to 18 is 90.

Step-by-step explanation:

For finding the sum (S) of n terms we use the formula,

Sn = (n/2) × (2a + (n-1)d)

The values of a, d and n are:

a = 2 (the first term)

d = 2 (the "common difference" between terms, as the difference between two even numbers is 2)

n = 9 (number of terms to add up)

We have found the number of terms by counting the even numbers between 2 and 18 including both 2 and 18

Using the formula,

Sn = (9/2) x (2(2) + (9–1)x2))

Sn = (9/2) x (4 + 16)

Sn = (9/2) x 20

Sn = 9 x 10

Sn = 90

So,the sum of even numbers from 2 to 18 is 90.

Answer 2

$\large \underline{ \underline{ \sf \: Solution : \: \: \: }}$

Given ,

AP : 2 , 4 , 6 , 8 , 10 , 12 , . . . . , 36

The first term (a) = 2

The common difference (d) = 2

Total number of terms (n) = 18

The last term (l) = 36

We know that ,

$\large \fbox{ \fbox{\sf sum = \frac{n}{2}(a + l)}}$

$\sf \to sum = \frac{18}{2} x (2 + 36) \\ \\ \sf \to sum = </p><p> \frac{18 \times 38}{2} \\ \\ \sf \to sum = \frac{684}{2} \\ \\ \sf \to sum = </p><p>342$

$\therefore$342 is the sum of first 18 even numbers