4+7+10+13+…..+334
T1=3*1+1
T2=3*2+1
T3=3*3+1
T4=3*4+1
…………
Tn=3*n+1
334=3*111+1
Deci, sunt 111 termeni.
T1+T2+T3+.....+Tn=(T1+Tn)*n/2
4+7+10+13+…+334=
=(4+334)*111/2
=338*111/2
=169*111
=18759
Sau:
3+7+10+13+….+334
=(3*1+1)+ (3*2+1)+ (3*3+1)+ (3*4+1)+….+ (3*111+1)
=3(1+2+3+….+111)+1+1+…..+1; 1 de 111 ori
=3*111*112/2+111
=333*56+111
=18648+111
=18759