Given-that-r-0-4-6r-2-r-1-n-5r-work-out-the-value-of-n-

Question Number 77953 by pete last updated on 12/Jan/20

Given that \underset{r = 0}{\sum^{4}} 6 r = 2 \underset{r = 1}{\sum^{n}} 5 r, work out the value

of n .

Answered by john santu last updated on 12/Jan/20

\underset{0}{\sum^{4}} (\frac{3}{5}) r = \underset{r = 1}{\sum^{n}} r

\frac{3}{5} (0 + 1 + 2 + 3 + 4) = \frac{n}{2} (n + 1)

12 = n^{2} + n \Leftrightarrow n^{2} - n - 12 = 0

n = 4, n = - 3 (n o s o l u t i o n)

Commented by pete last updated on 12/Jan/20

thanks but i dont understand please .

kindly do some explaining for me .

Answered by JDamian last updated on 12/Jan/20

3 \underset{r = 0}{\sum^{4}} r = 5 \underset{r = 1}{\sum^{n}} r

3 \frac{0 + 4}{2} 5 = 5 \frac{n + 1}{2} n

12 = n (n + 1)

n^{2} + n - 12 = 0

Commented by pete last updated on 12/Jan/20

thanks sir

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