Question

найдите промежуток, которому принадлежит сумма x+y

Answer 1

Ответ:   D ; F .

$\left\{\begin{array}{l}\dfrac{1}{x}+\dfrac{1}{y}=4\\\dfrac{2}{x}-\dfrac{3}{y}=-2\end{array}\right\ \ \left\{\begin{array}{l}t=\dfrac{1}{x}\\p=\dfrac{1}{y}\end{array}\right\ \ \left\{\begin{array}{l}t+p=4\ |\cdot 3\\2t-3p=-2\end{array}\right\ \oplus \ \left\{\begin{array}{l}p=4-t\\5t=10\end{array}\right$

$\left\{\begin{array}{l}p=4-2=2\\t=2\end{array}\right\ \ \left\{\begin{array}{l}\dfrac{1}{y}=2\\\dfrac{1}{x}=2\end{array}\right\ \ \left\{\begin{array}{l}y=\dfrac{1}{2}\\x=\dfrac{1}{2}\end{array}\right\ \ \left\{\begin{array}{l}y=0,5\\x=0,5\end{array}\right\\\\\\Otvet:\ (\, 0,5\ ;\ 0,5\ )\ ,\ \ x+y=1\in (-3,4)\ ,\ \ x+y=1\in (-24;5)\ .$