If you square the left hand side, you get
[tex] (3x)^2 = 3^2x^2 = 9x^2 [/tex]
You can expand the right hand side by multiplying both terms by 8:
[tex] 8(x-1) = 8x-8 [/tex]
So, the equation becomes
[tex] 9x^2=8x-8 [/tex]
Subtract the right hand side to move it to the left
[tex]9x^2-8x+8 = 0[/tex]
