Решите уравнение : (20-у) (7-у)=0

[latex](20-y)(7-y)=0[/latex][latex]140-20y-7y+ y^{2} =0[/latex][latex] y^{2} -27y+140=0[/latex][latex]D= (-27)^{2} -4*1*140=729-560=169[/latex][latex] x_{1} = frac{27+ sqrt{169} }{2} = frac{27+13}{2} = frac{40}{2} =20[/latex][latex] x_{2} = frac{27-13}{2} =7[/latex]