[tex]1 + 2 + 3 + ... + 105 = \\ \\ = \frac{105 \times 106}{2} = \\ \\ = \frac{11130}{2} = \\ \\ = 5565[/tex]
[tex]6 +12 + 18 + ... + 258 = \\ \\ = 6(1 + 2 + 3 + ... + 43) = \\ \\ = 6 \times \frac{43 \times 44}{2} = \\ \\ 6 \times \frac{1892}{2} = \\ \\ = 6 \times 946 = \\ \\ = 5676[/tex]
restul sunt in poză
BAFTĂ!!!
