A(6x-1)(x+1)=20 помогите решит

6х*х+6х-х-1=206х^2+5х-21=0D=25+4*6*21=529x=(-5+-√529)/12= 1.5

(6x - 1)(x + 1) = 206x² + 6x - x - 1 = 206x² + 5x - 21 = 0D = b² - 4ac = 25 - 4*6*(-21) = 25 + 504 = 529 = 23²x1 = ( - 5 + 23) / 12 = 1,5x2 = ( - 5 - 23) / 12 = - 28/12 = - 7/3