Math, asked by rima20048, 10 months ago


(viii) given a = 4, d=2, S = -14, find n and a.​

Answers

Answered by nikiju
32

Answer:

an= 4

d= 2

Sn=-14

a=?

n=?

an = a+(n-1)d

4 = a + ( n-1)2

4 = a + 2n - 2

6 = a + 2n

6 -2 n = a .........(1)

Sn= n/2 ( a + an )

-14 = n/2 ( 6-2n + 4 )

-28 = n ( 10 -2n )

-28= 10n -2n^2

2n ^2 -10n -28 =0

Divide by 2

n^2 -5n -14 =0

n ^2 -7n +2n -14 =0

n ( n-7) + 2 ( n-7)=0

( n-7) ( n+2)=0

n=-2 And n = 7

n is neither be negative. Putting n=7 in equation. (1)

a= 6- 2(7)

a= 6 -14

a= -8

Therefore, a=-8 & n=7

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Answered by Happiness07
3

Answer:

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