Question

Calculeaza B-A ,unde A=1+3+5+.….+25 si B=2+6+10+....+50​

Answer 1

A = 1+3+5+...+25

Formula in acest caz este

1+3+5+...+ (2n-1) = n*n

25 = 2*13-1 = 26-1 = 25

n = 13

A = 13 * 13 = 169

B = 2+4+6+...50

Factor comun si apoi

aplicam suma lui Gauss

2(1+2+3+...+25) = 2[(25*26)/2]

2(25*13) = 325 * 2

B = 325 * 2 = 650

B - A = 650 - 169 = 481