Odpowiedź :
[tex]Zadanie\\\\c=\frac{a+b}{2}\ \ \ \mid\cdot2\\\\2c=a+b\ \ \ \mid-b\\\\2c-b=a\\\\a=2c-b[/tex]
[tex]c = \frac{a+b}{2} / * 2[/tex]
[tex]2c = a + b / - b[/tex]
[tex]a = 2c - b[/tex]
[tex]Zadanie\\\\c=\frac{a+b}{2}\ \ \ \mid\cdot2\\\\2c=a+b\ \ \ \mid-b\\\\2c-b=a\\\\a=2c-b[/tex]
[tex]c = \frac{a+b}{2} / * 2[/tex]
[tex]2c = a + b / - b[/tex]
[tex]a = 2c - b[/tex]