Question

(vi) given a=2, d=8, S =90, find n and a,;
vi given a = 8.4 = 62. S = 210, find n and d.​

Answer 1

Step-by-step explanation:

a=2,d=8,s

n

=90

s

n

=

2

n

[2a+(n−1)d]

90=

2

n

[4+(n−1)8]

180=n[8n−4]

180=8n

2

−4n

=8n

2

−4n−180=0

=2n

2

−n−45=0

=2n

2

−10n+9n−45=0

=2n(n−5)−9(n−5)

an=(2n−9)(n−5)

n=5

an =a+(n−1)d

an =2+(5−1)8

an=2+3+4

an =34

hers your answer

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