3x^2-11x+15=0
D = 121-180 <0 решений нет
15x^2+11x+2=0
D = 121 - 120 = 1
x₁ = (-11+1)/30 = -⅓; x₂ = (-11 - 1)/30 = - 12/30 = -⅖
7x^2-3x=0
x(7x-3) = 0
x₁ = 0; x₂ = 3/7
1) D=121-180<0 корней нет
2) D= 121-120=1
x= (-11+1)/30=-1/3
x= (-11-1)/30=-12/30=-2/15
3) x(7x-3)=0
x=0 x= 3/7
