Find the sum of the first 10 terms. 40,37,34,31,...
2 answers:
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Putting this as an arithmetic sequence gives:
The sum of the series = 16 x 7 x 7 = 784 m^3 = 784 000 L
The sum of an arithmetic series can be written as:
![S_n=n/2 [2a+(n-1)d] = 784 000 \\n/2[2(150)+(n-1)200] = 784 000 \\n[300+200(n-1)=1 568 000 \\300n+200n^2-200n = 1 568 000 \\200n^2+100n- 1 568 000 = 0 \\2n^2 +n- 15680 = 0 \\n= 88.2...,-88.7](https://tex.z-dn.net/?f=S_n%3Dn%2F2%20%5B2a%2B%28n-1%29d%5D%20%3D%20784%20000%0A%5C%5Cn%2F2%5B2%28150%29%2B%28n-1%29200%5D%20%3D%20784%20000%0A%5C%5Cn%5B300%2B200%28n-1%29%3D1%20568%20000%0A%5C%5C300n%2B200n%5E2-200n%20%3D%201%20568%20000%0A%5C%5C200n%5E2%2B100n-%201%20568%20000%20%3D%200%0A%5C%5C2n%5E2%20%2Bn-%2015680%20%3D%200%0A%0A%5C%5Cn%3D%2088.2...%2C-88.7)
n has to be positive, so we get
n = <u>88.2 hours (3 s.f.)</u>
The sum of the series = 16 x 7 x 7 = 784 m^3 = 784 000 L
The sum of an arithmetic series can be written as:
n has to be positive, so we get
n = <u>88.2 hours (3 s.f.)</u>