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Question Number 94096 by Rio Michael last updated on 16/May/20
The result of adding the odd natural numbers is:               1 = 1          1 + 3=4    1 + 3+ 5 = 9  1 + 3 + 5 +7 = 16  1 + 3 + 5 + 7+9 = 25   show that from this result, Σ_(i=1) ^n (2i−1) = n^2 .
$$\mathrm{The}\:\mathrm{result}\:\mathrm{of}\:\mathrm{adding}\:\mathrm{the}\:\mathrm{odd}\:\mathrm{natural}\:\mathrm{numbers}\:\mathrm{is}: \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:\mathrm{1}\:=\:\mathrm{1} \\ $$$$\:\:\:\:\:\:\:\:\mathrm{1}\:+\:\mathrm{3}=\mathrm{4} \\ $$$$\:\:\mathrm{1}\:+\:\mathrm{3}+\:\mathrm{5}\:=\:\mathrm{9} \\ $$$$\mathrm{1}\:+\:\mathrm{3}\:+\:\mathrm{5}\:+\mathrm{7}\:=\:\mathrm{16} \\ $$$$\mathrm{1}\:+\:\mathrm{3}\:+\:\mathrm{5}\:+\:\mathrm{7}+\mathrm{9}\:=\:\mathrm{25} \\ $$$$\:\mathrm{show}\:\mathrm{that}\:\mathrm{from}\:\mathrm{this}\:\mathrm{result},\:\underset{{i}=\mathrm{1}} {\overset{{n}} {\sum}}\left(\mathrm{2}{i}−\mathrm{1}\right)\:=\:{n}^{\mathrm{2}} . \\ $$
Commented by Kunal12588 last updated on 16/May/20
sum of A.P.
$${sum}\:{of}\:{A}.{P}. \\ $$
Answered by Kunal12588 last updated on 16/May/20
Σ_(i=1) ^n (2i−1)=2Σ_(i=1) ^n i−n=2×((n(n+1))/2)−n  =n^2 +n−n=n^2
$$\underset{{i}=\mathrm{1}} {\overset{{n}} {\sum}}\left(\mathrm{2}{i}−\mathrm{1}\right)=\mathrm{2}\underset{{i}=\mathrm{1}} {\overset{{n}} {\sum}}{i}−{n}=\mathrm{2}×\frac{{n}\left({n}+\mathrm{1}\right)}{\mathrm{2}}−{n} \\ $$$$={n}^{\mathrm{2}} +{n}−{n}={n}^{\mathrm{2}} \\ $$
Commented by Rio Michael last updated on 16/May/20
perfect
$$\mathrm{perfect} \\ $$

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