Question

given a = 2, d = 8, S = 90, find n and an
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Answer 1

Answer:

hey mate here is the answer

Step-by-step explanation:

90= n/2(2×2+(n-1)×8)

90×2 = 4n+n(n-1)×8

180= 4n +8n²-8n

180= 8n²-4n

45= 2n²-n

2n²-n-45= 0

2n²-10n+9n-45=0

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

2n+9=0

n= 9/2

n-5= 0

n= 5

an= a+(n-1) d

= 2+(5-1)8

= 2+32= 34

ans - n= 5 and an= 34