Question

X=1+3+5...+49 , aflați x.

Answer 1

x=1+3+5+....+49(facem grupe)
x=50*12
x=600 asa cred eu

Answer 2

Aplicam formula:

1+3+5+...+(2k-1)=k^2, k>0

1+3+5+...+49=25^2

Sau:

X=1+3+...+49=(1+2+3+4+...+49)-(2+4+6+...+48)=

(1+2+3+4+...+49)-2(1+2+3+...+24)=

Aplicam:1+2+3+...+n=n(n+1)/2

49*50/2-2*24*25/2=49*25-24*25=25(49-24)=25*25=25^2