how many terms of the series 2,4,6,......must be taken in order that the sum may be 420?
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Answered by
5
2+4+6............38+40=420
hence we have to take this series to number 40 and terms 20 to obtain 420.
hence we have to take this series to number 40 and terms 20 to obtain 420.
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Answered by
8
ap=2,4,6
d=2
Sn=420
we have to find n
Sn=n/2 (2a+(n-1)d)=420 a=2
n( 4 + (n-1) 2)=840 d-2
n(4 + 2n-2) =840
n( 2n+2) = 840
2n²+2n -840=0
n²+n-420=0
n=20,-21
since n is positive number of terms needed are 20
so if we take 20 terms of the AP=2,4,6
we could get the sum 420
d=2
Sn=420
we have to find n
Sn=n/2 (2a+(n-1)d)=420 a=2
n( 4 + (n-1) 2)=840 d-2
n(4 + 2n-2) =840
n( 2n+2) = 840
2n²+2n -840=0
n²+n-420=0
n=20,-21
since n is positive number of terms needed are 20
so if we take 20 terms of the AP=2,4,6
we could get the sum 420
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