Asked by Olaitan
How many terms of the sequence 1+2+3+4.... are needed to make a sum of 820
Answers
Answered by
Olaitan segun
Sn=n/2 (2a + n-1)d
820=n/2(2(1)+(n-1)1)
820×2= n(2+(n-1)1)
1640= n(2+n-1)
1640=n(2-1+n)
1640= n(1+n)
1640= n+ n²
1640-n-n²=0
n²+n-1640=0
n²+41n-40n-1640 =0
n(n+41)-40(n+41)=0
n-40 =0 or n+41=0
n=40 or n= -41
That is, 14 terms are needed to make sum of 820
820=n/2(2(1)+(n-1)1)
820×2= n(2+(n-1)1)
1640= n(2+n-1)
1640=n(2-1+n)
1640= n(1+n)
1640= n+ n²
1640-n-n²=0
n²+n-1640=0
n²+41n-40n-1640 =0
n(n+41)-40(n+41)=0
n-40 =0 or n+41=0
n=40 or n= -41
That is, 14 terms are needed to make sum of 820
Answered by
oobleck
all that work, and you type the wrong answer at the end!
There are no AI answers yet. The ability to request AI answers is coming soon!
Submit Your Answer
We prioritize human answers over AI answers.
If you are human, and you can answer this question, please submit your answer.