Question

помогите пожайлуста срочно решить ​

Answer 1

$\left \{ {{\frac{20}{x+y} +\frac{20}{x-y} =7} \atop {\frac{5}{x+y} =\frac{2}{x-y} }} \right.$

 Замена:

$\frac{1}{x+y}=a ;$    $\frac{1}{x-y}=b$

$\left \{ {{20a+20b=7} \atop {5a=2b}} \right.$

$\left \{ {{20a+20b=7} \atop {a=0,4b}} \right.$

$20*0,4b+20b=7$

$8b+20b=7$

$28b=7$

$b=\frac{7}{28}=\frac{1}{4}$

при $b=\frac{1}{4}$    =>   $a=\frac{0,4}{4}=0,1=\frac{1}{10}$

Обратная замена:

 $\left \{ {{\frac{1}{x+y} =\frac{1}{10} } \atop {\frac{1}{x-y} =\frac{1}{4} }} \right. =>\left \{ {{x+y =10} \atop {x-y =4 }} \right. =>\left \{ {{x+y =10} \atop {x=y +4 }} \right. =>\left \{ {{y+4+y =10} \atop {x=y +4 }} \right. =>\left \{ {{y=3} \atop {x=y +4 }} \right. =>\left \{ {{y=3} \atop {x=7 }} \right.$

    $x=7$

    $y=3$

Ответ:  (7;  3)