in an A.P, if a1 = -2, d=5,sn =568,then find 'n' ,'l'.
Answers
Hey mate here is ur answer----
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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!!!
Answer:
Step-by-step explanation:
Hey mate here is ur 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!!!