Odpowiedź :
[tex]x + 2 \times x + 3 \times x + ... + 15 \times x - 3 = 9[/tex]
[tex]x + 2x + 3x + ... + 15x - 3 = 9[/tex]
[tex]x + 2x + 3x + ... + 15x = 12[/tex]
„...” - to dalszy ciąg od 4x do 14x
[tex]x + 2x + 3x + 4 x + 5x + 6x + 7x + 8x + 9x + 10x + 11x + 12x + 13x + 14x + 15x = 12[/tex]
[tex]120x = 12[/tex]
[tex]x = \frac{12}{120} = \frac{1}{10} [/tex]