Răspuns :
S=7+14+21+28+....+210
S=7*(1+2+3+4+....+30)
S=7*30*31:2
S=7*15*31
S=7*465
S=3255
S=7*(1+2+3+4+....+30)
S=7*30*31:2
S=7*15*31
S=7*465
S=3255
7+14+21+28+210 egal cu 7 (1+2+3+4+....+30)
7*(30*31/2) egal 7*(15*31)egal 7*465 egal3255
7*(30*31/2) egal 7*(15*31)egal 7*465 egal3255