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]