Question

write the algebra of 10, 18, 26 also calculate the sum of first 30 terms

Answer 1

$since \\ sn \: = n \div 2(2a + nd - d )$
here n = 30 , a = 10 ., d = 8
then Sn = 30/2 ( 20 + 240 - 8 )
15 ( 260 - 8 )
15 ( 252 )
3780 .///

Answer 2

Series = 10, 18, 26 ....

⇒ First term = a1 = 10

⇒ common difference = 18 - 10 = 8

Find the nth term:

an = a1 + (n - 1)d

an = 10 + (n - 1)8

an = 10 + 8n - 8

an = 2 + 8n

Find the 30th term:

a30 = 2 + 8(30)

a30 = 242

Find the sum of the first 30 terms:

sn = n/2 (a1 + an)

s30 = 30/2 (10 + 242) = 3780

Answer: 3780