Răspuns :
3(21+22+23+...+179)=
3(1+2+3+...+179-1-2-3-...-20)
3(179*180/2-20*21/2)
3(179*90-210)=
3(16110-210)=
3*15900=47700
3(1+2+3+...+179-1-2-3-...-20)
3(179*180/2-20*21/2)
3(179*90-210)=
3(16110-210)=
3*15900=47700