Question

a=2 d=8 sn=90 find n and tn​

Answer 1

Answer:

Sn = n / 2 ( 2a + ( n - 1 )d )

90 = n / 2 ( 2 × 2 + ( n - 1 )8 )

180 = n ( 4 + 8n - 8 )

180 = n ( 8n - 4 )

180 = 8n2 - 4n

8n2 - 4n - 180 = 0

4(n2 - n - 180) = 0

2n2 - n - 45 = 0

2n2 - 10n + 9n - 45 = 0

2n ( n - 5 ) + 9 ( n - 5 ) = 0

( 2n + 9 ) ( n - 5 ) = 0

n = 5

an = a + ( n - 1 )d

an = 2 + ( 5 - 1 )8

an = 2 + 4 x 8

an = 34

Hope it helps ..!!

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