Question

calculati urmatoarele sume : a)1+2+3+.....80

Answer 1

1+2+3+.............+80=
=[80×(80+1)]÷2
=(80×81)÷2
=3240

Answer 2

$\displaystyle 1+2+3+...+80= \frac{80(80+1)}{2} = \frac{80 \times 81}{2} = \frac{6480}{2} =3240$