2 < а < 5 |*4

8 < 4а < 10

1 < b < 3 |*(-1)

-1 > -b > -3

-3 < -b < -1

8 + (-3) < 4a - b < 10 + (-1)

5 < 4a - b < 9

[tex]\displaystyle\bf \\ 2 < a < 5 \: \: | \times 4 \\ 8 < 4a < 20 \\ \\ 1 < b < 3 \: \: | \times ( - 1)\\ - 1 > - b > - 3 \\ - 3 < - b < - 1 \\ \displaystyle\bf\\ + \left \{ {{8 < 4a < 20} \atop { - 3 < - b < - 1 }} \right. \\ \\ 8 - 3 < 4 a - b < 20 - 1 \\ 5 < 4a - b < 19[/tex]