Question

1+3+5...+47+48+49 ? Repede vă rog , dau coroană . ​

Answer 1

 

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):

$\displaystyle\bf\\n=\frac{49-1}{2}+1=\frac{48}{2}+1=24+1=25~de~termeni$

Calculam suma:

$\displaystyle\bf\\1+3+5+...+45+47+49 =\frac{n(49+1)}{2}=\\\\=\frac{25\times50}{2}=25\times25=\boxed{\bf25^2}=\boxed{\bf625}$