Question

se considera numerele: x = 1+2+3+...+20, y = 2+4+6+...+40 si z = 3+6+9+...+60 Calculeaza x+y+z

Answer 1

x = 1+2+3+...+20 = 20x21:2 = 210
y = 2+4+6+...+40 = 2(1+2+..+20) = 20x21 = 420
z = 3+6+9+...+60 = 3(1+2+..+20) = 3x20x21:2 = 630

x+y+z = 210 + 420 + 630  =1260

Answer 2

x=1+2+3+....+20
1+2+3+...+20= 20x(20+1):2=(20x21):2=420:2=210
x=210

y=2+4+6+...+40
dam pe 2 factor comun
y=2 (1+2+3+...+20)
y=2x210
y=420

z=3+6+9+...+60
dam pe 3 factor comun
z = 3(1+2+3+...+20)
z=3x210
z=630
x+y+z=210+420+630=1260