Question

решить систему уравнений
2) x + y = 9
x*y = 10

Answer 1

$\left \{ {{x+y=9} \atop {x\cdot y=10}} \right. \left \{ {{y=9-x} \atop {x\cdot (9-x)=10}} \right. \left \{ {{y=9-x} \atop {9x-x^2=10}} \right. \left \{ {{y=9-x} \atop {-x^2+9x-10=0}} \right. \left \{ {{y=9-x} \atop {x^2-9x+10=0}} \right. \\ \\ x_{1,2}=\frac{-(-9)\pm\sqrt{(-9)^2-4\cdot 1 \cdot 10 }}{2\cdot 1}=\frac{9\pm\sqrt{81-40}}{2}=\frac{9\pm\sqrt{41}}{2} \\ \\ y_1=9-\frac{9+\sqrt{41}}{2}=\frac{9-\sqrt{41}}{2} \\ \\ y_2=9-\frac{9-\sqrt{41}}{2}=\frac{9+\sqrt{41}}{2}$