Step-by-step explanation:
[tex] {x}^{2} = \frac{mn + 1}{9} [/tex]
[tex](3x - 1)(3x + 1)[/tex]
[tex]9 {x}^{2} - 1[/tex]
[tex] {x}^{2} = \frac{9 {x}^{2 } - 1 + 1 } {9} [/tex]
[tex] {x}^{2} = \frac{9 {x}^{2} }{9} [/tex]
[tex] {x}^{2} = {x}^{2} [/tex]
So this identity is true.
