Odpowiedź:
c = 2x + y /-y
c - y = 2x /:2
(c - y): 2 = x
[tex]c\ =\ 2x+y\\2x+y = c /+(-y)\\2x = c-y/:2\\\\x = \frac{1}{2} c + \frac{-1}{2} y[/tex]