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90 = (n/2)(4+(n-1)8)

180 = n(8n-4)

180 = 8n^2-4n

8n^2-4n-180 = 0

n=5

An = 2+4*8=34

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

⇒ 90= n/2[2x2+(n-1)x 8]

⇒90 = n/2[4+8n-8]

⇒90 = n/2x2[2+4n-4] [then 2 and 2 will be cancel]

⇒90 = 2n +4n²-8n

⇒90 = -6n +4n²

⇒4n²-6n -90 =0

⇒ 4n² - 20n+18n -90=0

⇒2n(2n-10)+9(2n-10) =0

⇒(2n+10) (2n+9)

n=-9/2 ,5

lets take n=5

an=2+(n-1)x d

a5=2 + (5-1)x 8

= 2+4 x 8

= 2+32

=34

so,the an=34 and n=5