Question

Calculati sumele:
S1= 1-2+3-4+5-....+99-100
S2= -2-4-6-....-98-100
COROANA!!

Answer 1

S1=(-1-1-...-1)•100:2 S1=-50 S2=-2(1+2+...+50) S2=-2•50•51:2 S2=-2550

Answer 2

$S_{1} =(1-2)+(3-4)+(5-6)+...(99-100)=-1-1....-1=-50 \\ S_{2} =-2(1+2+...+50)=-2\cdot \frac{50 \cdot 51}{2}=-2550$