log(7)(2x^2-5x+31)=2
2x^2 - 5x + 31 = 7^(2) 2x^2 - 5x - 18 = 0 D=25-4*2*(-18) = 169 x_(1)= (5 - 13)/4 = - 2 ; x_(2)= (5+13)/4=9/2