Explicație pas cu pas:
b)
[tex](x - 1) + (x - 2) + (x - 3) + ... + (x - 20) = 0 \\ [/tex]
[tex]x + x + ... + x - (1 + 2 + 3 + ... + 20) = 0 \\ [/tex]
[tex]20x = 1 + 2 + 3 + ... + 20[/tex]
[tex]20x = \frac{20 \cdot 21}{2} \implies \bf x = \frac{21}{2} \\ [/tex]
c)
[tex]x - 2x + 3x - 4x + ... + 99x - 100x = 500 \\ [/tex]
[tex](x - 2x) + (3x - 4x) + ... + (99x - 100x) = 500 \\ [/tex]
[tex]( - x) + ( - x) + ... + ( - x) = 500[/tex]
[tex]- 50x = 500 \implies \bf x = - 10[/tex]
