Odpowiedź :
[tex]Zadanie\\\\\frac{a_1+a_3}{2} =a_2\\\\\frac{x+3x-1}{2}=7\ \ \ \mid\cdot2\\\\4x-1=14\ \ \ \mid+1\\\\4x=15\ \ \ \mid:4\\\\x=\frac{15}{4}\\\\Odp.\ "1"[/tex]
[tex]Zadanie\\\\\frac{a_1+a_3}{2} =a_2\\\\\frac{x+3x-1}{2}=7\ \ \ \mid\cdot2\\\\4x-1=14\ \ \ \mid+1\\\\4x=15\ \ \ \mid:4\\\\x=\frac{15}{4}\\\\Odp.\ "1"[/tex]