А) 9x^2-1=0 9x^2=1 x^2=1/9 x=1/3 x=-1/3 б)x^2=8x x^2-8x=0 x(x-8)=0 x=0 x=8 в) x^2-9x+20=0 x12=(9+-корень(81-80))/2=(9+-1)/2=4 5 x=4 x=5