Question

given a=2,d=8,Sn=90 find n and An

Answer 1

нєℓℓσ ∂єαя υѕєя!!!!



gívєn quєѕtíσn :


Given a=2, d=8, Sn=90 find n and An



αnѕwєr :



Given;

An= a+ (n-1)d

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


90 = (n/2)(4+(n-1)8) 


180 = n(8n-4) 


180 = 8n²-4n 


8n²-4n-180 = 0 



n=5 



An = 2+4*8

=34



THΣRΣҒΩRΣ THΣ ∇ΔLUΣ ΩҒ n IS 5
ΔΠD An IS 34



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Answer 2

Answer:

Sn = (n/2)(2a+(n-1)d)  

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