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\(\left(1-\frac{1}{n}\right)+\left(1-\frac{2}{n}\right)+\left(1-\frac{3}{n}\right)+... up to n terms = ?\)

Options:
A .  (n−1)
B .  \(\frac{n}{2}\)
C .    \(\frac{1}{2}\) (n−1)
D .   \(\frac{1}{2}\)  (n+1)
Answer: Option C

\(\left(1-\frac{1}{n}\right)+\left(1-\frac{2}{n}\right)+\left(1-\frac{3}{n}\right)+... up to n terms \) 


= \(\left(1+1+1+... up to rerms \right) - \left(\frac{1}{n}+\frac{2}{n}+\frac{3}{n}+...up to rerms\right)\)


= \(n-\frac{1}{n}\left(1+2+3+...up to rerms\right)\)


= \(n-\frac{1}{n}\left[\frac{n(n+1)}{2}\right]\)


= \(n-\frac{(n+1)}{2}\)


= \(\frac{(2n-n-1)}{2}\)   


= \(\frac{n-1}{2}\)


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2 Comments

coma very happy good
Solution also

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