Question

given a=4 d=5 an=89 find n and sn ?
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Answer 1

Step-by-step explanation:

a=4

d=5

an=89

an=a+(n-1)d

89 = 4+(n-1)5

89 = 4+5n-5

89 = 5n-1

5n=90

n= 90/5

n= 18

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

sn =18/2 [ 2(4)+(18-1)5]

sn= 9 [ 8+85]

sn = 837

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