Question

In an A.P , if a1 = - 2, d = 5, sn = 568, then find 'n' , 'l' .​

Answer 1

Answer:

568=n/2(-2+5n-7). putting Lbvalue here. putting this n value in L value above .. So the L value or( last term)is =73.

Answer 2

Answer:

L=a+(n-1)d

L=-2+(n-1)5

L=-2+5n-5

L=5n-7

as sn is given=568

sn=n/2(a+l)

568=n/2(-2+5n-7). putting Lbvalue here.

1136=n(5n-9)

1136=5n²-9n

5n²-9n-1136=0

5n²-80n+71n-1136=0

5n(n-16)+71(n-16)

n-16=0

n=16

So the n value is 16

putting this n value in L value above ..

L=5n-7

L=5*16-7

L=80-7

L=73...

So the L value or( last term)is =73.

n=16...Ans

Hope it helps to you!!!

Step-by-step explanation:

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