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Demonstreaza ca mr a este este patrat perfect , unde a=1+2+3.....+100+51×101

Răspuns :

[tex]a=1+2=3+...+100+51 \cdot 101= \\ \\ ~~~= \frac{100 \cdot 101}{2} +51 \cdot 101= \\ \\ ~~~=50 \cdot 101+51 \cdot 101= \\ \\ ~~~=101(50+51)= \\ \\ ~~~=101 \cdot 101= \\ \\ ~~~=101^2-~patrat~perfect.[/tex]
[tex]a=1+2+3.....+100+51*101= \frac{101*100}{2}+51*101[/tex] [tex]=101*50+51*101 = 101(50+51) = 101*101 = 101^2[/tex] ⇒ a = p.p.