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SIZIF [17.4K]
3 years ago
6

Find the sum of this problemOptions:52 26 13 32

Mathematics
1 answer:
Ad libitum [116K]3 years ago
4 0
\displaystyle\sum_{i=3}^{10}(2i-9)=2\sum_{i=3}^{10}i-9\sum_{i=3}^{10}1
\displaystyle=2\left(\sum_{i=1}^{10}i-\sum_{i=1}^2i\right)-9\left(\sum_{i=1}^{10}-\sum_{i=1}^21\right)

Recall that

\displaystyle\sum_{i=1}^ni=\frac{n(n+1)}2
\displaystyle\sum_{i=1}^n1=n

so the above reduces to

2\left(\dfrac{10\cdot11}2-\dfrac{2\cdot3}2\right)-9\left(10-2\right)=32

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