[tex]y = 9 - x[/tex]
Substitute into
[tex]y \times x = 20 \\ (9 - x) \times x = 20 \\ { - x}^{2} + 9x = 20 \\ {x}^{2} - 9x + 20 = 0 \\ (x - 5)(x -4) = 0 \\ x = 5 \: or \: x = 4[/tex]
When x = 5,
[tex]y = 9 - 5 \\ y = 4[/tex]
When x = 4,
[tex]y = 9 - 4 \\ y = 5[/tex]
x = 5, y = 4
x = 4, y = 5
Hope this helps. - M
