how many terms of arithmetic sequence 7,11,15.... starting from the first be added to get 900?
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Step-by-step explanation:
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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
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