Question

Розв’язати способом додаванням:
{2x+xy= -10
{y -xy =9

Answer 1

$\displaystyle\bf\\+\left \{ {{2x+xy=-10} \atop {y-xy=9}} \right.\\----------\\2x+y=-1\\\\y=-2x-1\\\\-2x-1-x\cdot(-2x-1)-9=0\\\\-2x-10+2x^{2} +x=0\\\\2x^{2} -x-10=0\\\\D=(-1)^{2} -4\cdot 2\cdot(-10)=1+80=81=9^{2} \\\\\\x_{1} =\frac{1-9}{4}=-2\\\\\\x_{2} =\frac{1+9}{4} =2,5\\\\\\y_{1} =-2\cdot(-2)-1=4-1=3\\\\\\y_{2} =-2\cdot 25-1=-5-1=-6\\\\\\Otvet \ : \ (2 \ , \ 3) \ , \ (2,5 \ ; \ -6)$