👤

cat face 4+7+10+13+16+...+1993


Răspuns :

4 = 3×1+1
7 = 3×2+1
10 = 3×3+1
.....
1993 = 3×664+1
3×n+1

4+7+10+13+16+...+1993 =
= 3(1+2+3+4+5+...+664) +1+1+...+1 =
de 664 ori
= 3×664×665:2 +1×664 =
= 662340+664 =
= 663004