1 + 3 + 5 + ... + 47 + 48 + 49 = ?
Enuntul contine o greseala:
Un numar par "48" intr-un sir de numere impare.
Voi corecta greseala.
Corect este:
1 + 3 + 5 + ... + 45 + 47 + 49 = ?
Rezolvare:
Calculam numarul de termeni (n):
[tex]\displaystyle\bf\\n=\frac{49-1}{2}+1=\frac{48}{2}+1=24+1=25~de~termeni[/tex]
Calculam suma:
[tex]\displaystyle\bf\\1+3+5+...+45+47+49 =\frac{n(49+1)}{2}=\\\\=\frac{25\times50}{2}=25\times25=\boxed{\bf25^2}=\boxed{\bf625}[/tex]
