Question

Произведение каких чисел дает 0.25, а сумму 1.8?

Answer 1

$\left \{ {{xy=0,25} \atop {x+y = 1,8}} \right. \\\\ \left \{ {{xy=0,25} \atop {y = 1,8 - x}} \right. \\\\ \left \{ {{x(1,8 - x)=0,25} \atop {y = 1,8 - x}} \right. \\\\ \left \{ {{1,8x - x^2=0,25} \atop {y = 1,8 - x}} \right. \\\\ \left \{ {{- x^2 + 1,8x -0,25 = 0} \atop {y = 1,8 - x}} \right. \\\\ \left \{ {{ x^2 - 1,8x + 0,25 = 0} \atop {y = 1,8 - x}} \right. \\\\ \left \{ {{ X_{1,2} = \cfrac {1,8 \pm \sqrt{3, 24 - 1}}{2}} \atop {y = 1,8 - x}} \right. \\\\$
$\left \{ {{ X_{1,2} = \cfrac {1,8 \pm \sqrt{3, 24 - 1}}{2}} \atop {y = 1,8 - x}} \right. \\\\ \left \{ {{ X_{1,2} = \cfrac {1,8 \pm \sqrt{2, 24}}{2}} \atop {y = 1,8 - x}} \right. \\\\ \left \{ {{ X_{1,2} = \cfrac {1,8 \pm \sqrt{2, 24}}{2}} \atop {y_{1,2} = 1,8 - \cfrac{1,8 \pm \sqrt{2, 24}}{2}}} \right. \\\\$

$\left \{ {{ X_{1,2} = \cfrac {1,8 \pm \sqrt{2, 24}}{2}} \atop {Y_{1,2} = \cfrac{1,8 \mp \sqrt{2, 24}}{2}}} \right. \\\\$

ответ:
$\cfrac {1,8 + \sqrt{2, 24}}{2}}$ и $\cfrac {1,8 - \sqrt{2, 24}}{2}}$

или 

$\cfrac {1,8 - \sqrt{2, 24}}{2}}$ и $\cfrac {1,8 +\sqrt{2, 24}}{2}}$

что по сути то же самое