Dam factor comun:
a) 3×(1+2+3+4+.........+673)
=3×673×(673+1):2
=3×673×674:4
=3×673×337=680403
b)4(1+2+3+........+505)
=4×505(505+1):2....calculezi tu
c)5(1+2+3+4+.......+404)
=5×404(404+1):2....calculezi tu
d)7(1+2+3+......+289)
=7×289(289+1):2..calculezi tu
Sper ca te.am ajutat. coronita? :)
