Question

In A.p l=8,n=8,sn=-20 find n=??

Answer 1

Answer:

Last term, l = 8

No. of terms, n = 8

Sum of 8 terms S_8S

8

= -20

Now,

S_nS

n

= n/2 × [a+l]

S_8S

8

= 8/2 × [a+8]

-20 = 4 × (a+8)

a + 8 = -5

a = -13

Hence,

The first term, a = -13

Step-by-step explanation:

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