1+5+9+...± x is 1770 find X
Answers
Answered by
25
Answer:
Step-by-step explanation:
an=a+(n-1)d
X=1+(n-1)4
=1+4n-4
X =4n-3
Sn=n/2(a+an)
1770=n/2(1+4n-3)
1770×2=n(4n-2)
3540=4n^2-2n
4n^2-2n-3540=0
÷2 2n^2-n-1770=0
Sum=-1
Product =-1770×2=-3540
The numbers are = -60 , 59
(2n^2-60n)(+59n-1770)
2n(n-30)+59(n-30)
n-30=0 or 2n+59=0
n=30 or n= -59/2
n can't be negative .so n=30
Sub n=30 in x=4n-3
X =4×30-3
=120-3
X=117
Check
Sn=n/2(a+an)
Sn=30/2(1+117)
= 15×118
Sn =1770
Answered by
3
Step-by-step explanation:
an=a+(n-1)d
X=1+(n-1)4
=1+4n-4
X =4n-3
Sn=n/2(a+an)
1770=n/2(1+4n-3)
1770x2=n(4n-2)
3540=4n^2-2n
4n^2-2n-3540=0
-2 2n^2-n-1770=0
Sum=-1
Product =-1770x2=-3540
The numbers are = -60, 59
(2n^2-60n)(+59n-1770)
2n(n-30)+59(n-30)
n-30=0 or 2n+59=0
n=30 or n= -59/2
n can't be negative .so n=30
Sub n=30 in x=4n-3
X=4*30-3
=120-3
X=117
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