Question

how many terms of arithmetic sequence 7,11,15.... starting from the first be added to get 900?​

Answer 1

Step-by-step explanation:

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Answer 2

Answer:

a=7

d=11-7=4

sn=900

sn=n/2(2a+(n-1)d)

900=n/2(14+(n-1)4)

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

900=n/2(10+4n)

1800=n(10+4n)

1800=10n+4n²

=4n²+10n-1800

d=b²-4ac

=100+28800=28900

x=-b+underroot d/2a

= -10+170/8

=160/8

=20

20 is the answer